Pond Boss Forums GENERAL QUESTIONS Muddy water Turbidity tolerances of fish by species

My 1.5 acre pond is still settling, with more suspended particles than I'd prefer. This is due to currently inadequate vegetation on the shoreline, with current efforts to remedy this that aren't complete yet unfortunately.

A little background on the pond:
In November 2024, relatively small numbers of YP and SMB were introduced after a forage base of FHM and Eastern Silvery Minnows were established and supplemented by naturally occurring crayfish (at least a few different species), frogs and their tadpoles (tree frogs and a species called green frog, which looks like a somewhat smaller bullfrog) as well as GSH. My hope is to add brook trout when the turbidity settles out to a level that I'm confident they can tolerate.

Based on my water temps, the YP should be finishing their first spawn. The fish that were introduced were large enough that they should be capable of that this year. The SMB that were introduced averaged about 5", so I don't suspect they will be large enough to spawn this year.

I just had a Secchi disk delivered and have yet to get out with the kayak to get a reading. While I was waiting for it to arrive, I did what I could to educate myself on the effects of turbidity on my fishery, and thought I would share a bit of what I found and open the forum to discussion from the experiences of others.

Although a Secchi disk seems to be the preferred method of folks like us, there are more scientific methods of measuring turbidity, most of which use Nephelometric Turbidity Units (NTU) as their unit of measure. Despite my efforts, I couldn't find a correlation between Secchi disk readings and NTUs. Does anyone here happen to know what they are? I think this would be helpful, given that the published literature uses NTUs but mere mortals such as us use a Secchi disk.

Of the published research that I found on the topic of turbidity, here are a few interesting points that I came across. Most studies on freshwater fish tolerance to turbid conditions are done on streams and rivers, with much fewer done on lakes and ponds. A study done on the Great Lakes did sampling of fish via traps or electrofishing in water bodies of varying turbidity, with the assumption that species that were "present and abundant" in more turbid conditions equated to that species being tolerant to turbidity. Surprisingly, YP were listed in the category of the most tolerant to turbid conditions. Equally surprising, FHM were considered "moderately tolerant", less so than YP. Also in the "moderately tolerant" category were LMB, SMB, and GSH. They were in the same category as black and brown bullheads, which I have always thought to be one of the most resilient freshwater fish. Based on this study, YP exceeded bullheads in their tolerance for turbidity. Here is the study for anyone interested: https://www.researchgate.net/public...es_of_Great_Lakes_Coastal_Wetland_Fishes

Specifically for YP, I found a study that compared turbidity from sediment vs turbidity from algal blooms on survival and growth of YP up to one year old. Interestingly, higher turbidity from sediment during the youngest stages of life led to faster growth than either low turbidity or turbidity from algal blooms. They hypothesized that this was an effect of the focal length of the fish's eyes changing at varying stages of growth, with younger fish having increased visual contrast of prey items when sediment turbidity is present. Because YP fry were able to be more effective hunters in waters with sediment turbidity, they matured faster (underwent ontogenetic shift) than YP fry in clear waters or in turbid waters caused by algal blooms. This was not the case when they reached the "juvenile stage".

In this same study, turbidity caused by algal blooms led to decreased growth because "algal turbidity both scatters incoming light and selectively absorbs photosynthetically active radiation, thus reducing light levels more than sediment turbidity of the same intensity (Gallegos et al. 1990)," therefore YP fry were less able to see prey. Less successful hunting led to slower growth, longer times to reach ontogenetic shift, and more starvation leading to death. Even low levels of algal growth led to worse conditions in all stages of development studied (age-0). This seems counter to the common practice of fertilizing ponds to cause blooms. I'm curious to hear the feedback of the professionals as it relates to this. Here is the link to the publication of you'd like to read it.
https://www.researchgate.net/public...es_of_Great_Lakes_Coastal_Wetland_Fishes

Another study found BCP, BG, GSH and pumpkinseeds among the most tolerant of turbidity, with LMB, bullheads and YP considered "moderately tolerant". Moderately intolerant were SMB, BNM, CSH, BT and dace species. FHM were listed in the least tolerant category, which surprised me again. https://academic.oup.com/najfm/article/18/2/236/7862980

Since I'm hoping to add BT to the pond when it is clear enough that I'm comfortable doing so, I looked deeper into their tolerance of turbid water. A Canadian study I found assessed daily food consumption and growth rates at varying levels of turbidity. They found that trout ate the same despite water clarity levels, but those living in greater turbidity grew less. They hypothesized that the needed to actively hunt more to get the same amount of food, therefore they burned more calories from energy expenditure and put on less weight. https://cdnsciencepub.com/doi/10.1139/f00-260

I thought someone else may have some of the same questions that I had, so I thought I would share what I've learned.

Some questions that I wasn't able to answer are:
How does turbidity effect egg viability?
What is the conversion from Secchi disk readings to NTUs?
How does color staining by tannins impact turbidity readings? Waters around me are clear and brown, like ice tea.
How do the above studies in lakes and streams correlate to smaller impoundments such as ours?

I welcome your thoughts and experiences.

Mainer,

In addition to the BT performing better in less turbid water, similar observations of various other species have also been reported.

Any loss of clarity will work against spotting prey as it shortens visual reach. In theory this will reduce the number of encounters and opportunities for predatory attempts. When loss of clarity is caused by the production of phytoplankton, however, the enhanced food chain can produce more opportunities by supporting greater populations of prey. Muddy water, on the other hand, is a double whammy. It reduces production at the bottom of the food chain and shortens visual reach. So its harder to find the consequent lower populations of prey.

Too much weed coverage can also increase search times. The authors discussion around increased search times in turbid water reducing rest/handling periods makes a lot of sense to me.

JP: That seems to be the conventional wisdom (at least as it applies to BG/LMB stocking in the south), which is why I was a bit surprised to see that sediment turbidity actually caused an increase in growth and survival over algal turbidity when it comes to very young YP. I suspect that BG do better in algal turbidity than YP do, otherwise I would think that fertilization would be counter productive.

Maybe I'm missing something.

Secchi disk readings and NTU's have no conversion.
Secchi disk is YOUR eyes perspective, NTU is a refractive measurement and how UV bounces and reflects off of a dirt particle vs reflective single cell organisms.
Sight is a factor, but not the only factor.

How does turbidity effect egg viability? Turbidity itself is a product of suspended particulates, whether sediment or algal, it affects O2 to the eggs.
What is the conversion from Secchi disk readings to NTUs? There is no conversion as they are different factors in these measurements, but the secchi disk will provide the general measurement as a base-line
How does color staining by tannins impact turbidity readings? Waters around me are clear and brown, like ice tea. The secchi disk is the standard measurement.
How do the above studies in lakes and streams correlate to smaller impoundments such as ours? It's water, vis is vis and affects "X" species the same in both types in the same manner. Keep in mind, in rivers, the changes can be more rapid, both in declines and improvements.

Well it's not just you missing something ... how about me and the authors of the paper and findings that you referred to? That said, there must be some very reasonable reasons. I haven't a clue what they are for each individual case but what I do know is this. If YP are growing faster in higher sediment turbidity then they must individually be eating more in those cases of the waters studied. We know that it probably is not the sediment sustaining them unless that dirt has calories. So, the answer would lie in why water with higher sediment turbidity is providing more food to YP YOY than in other water. I'll offer some suggestions. And none of them could be the reason for the observation but each may be worthy of study.

1. There is less competition and lower numbers of YP.

2. There is less competition and lower numbers (or even the absence of) competing species.

3. There are prey items that contribute to turbidity (eg some may flies do) and these benefited YP due to their benthic feeding habits more than their competitors.

The best lake I’ve ever fished was extremely turbid. Although a public lake, very few people fished it; even locals. It was about 75 acres. We drove about 100 miles each direction, hauling Jon boats to fish it. Put your hand in the water and you couldn’t see your fingers. We called it the mud hole. The bass we caught had very little color, almost white but healthy and full of fight. I once tried a fly rod with a small bug and caught a bunch of whopper bluegills so I Believe the lake was pretty balanced re predator and prey.

We usually tossed big, noisy, spinner baits. Not much finesse involved. Somebody drowned there and they blocked off the boat ramp about 25 years ago. Haven’t fished it since but will never forget it.

Lots of good information here about water clarity. Five actually six main things commonly contribute to water visibility or clarity. 1. Suspended sediment, mud, dirt; 2. suspended organic detritus; 3. bacteria; 4. planktonic algae; 3. zooplankton; and 6. often water color or stain.

When one digs deep into the topic there have been a few comparisons made between secchi disk readings and NTU's plus some data about the two types or methods of measurements that I have gathered from information from Municipal water reservoirs. Generally the two readings are 'pretty' similar when plotted on a X-Y axis line. There are exceptions. I would post an example of one of the plotted data graphs but posting here is too inconvenient for my techy skills. If someone is willing I can send them one example graph for posting on this thread. Send me a PM.

I read the first study. The question is why are fish in a particular place at a particular time? I have questions about the results. Fish are where they are at a particular time for a multitude of reasons (not just turbidity). It is an AFS study so that is a +. The idea that fish turbidity tolerance can be measured by where fish are at a particular time and place is dubious to me. While I am a big believer in scientific studies they are often found to be lacking later on by subsequent findings. "It all depends" is often used and for good reason. Often years of experience by numerous skilled fisheries people is more trustworthy that one or two studies.

Here is a quote from the second study, also an AFS study, which I find more realistic "The tolerance of species to anthropogenic disturbances may be problematic because of the amount of judgment often required. To date, most developers of IBIs have used their professional judgment to assign tolerance classes, combining information from state fish books, personal experience, discussions with other professionals, conventional wisdom, and tolerance assignments from IBIs in other regions. We held informal discussions with several professionals who have developed IBIs and found that none had applied any quantitative methods in assigning species to overall tolerance classes."

Thoughts ? Are you by chance a scientist?

These graphs are provided by Bill Cody:

I apologize for my delay in getting back to you all, but thank you for the thoughtful replies. In re-reading this post, I saw that I posted the same link twice. The study that references increased growth (therefore increased consumption and/or less daily energy expenditure) with sediment turbidity vs algal turbidity is here. Sorry about that.
https://www.utoledo.edu/nsm/lec/research/im/docs/cjfas-2013-0528.pdf

If I'm understanding the results correctly, it is a fairly well designed study that indirectly argued against conventional wisdom of pond fertilization to induce an algal bloom. Here are a few of their concluding points:
"Cohorts modeled with high sediment turbidity had the highest larval growth rate and underwent the ontogenetic shift 5 days earlier, on average, than cohorts modeled with low sediment turbidity (Fig. 4a). However, the larval growth advantage did not continue into the
juvenile phase when sediment turbidity remained high; the low sediment fish quickly surpassed the high-sediment fish in length.
Fish produced in low-sediment conditions were 25% larger than those produced in high-sediment conditions (82 versus 63 mm, Fig. 4a) at 124 days. Higher total growth, however, did not confer higher survival, as high-sediment conditions produced the lowest starvation mortality rate (Fig. 4b).

Fish in algal turbidity grew more slowly than those in sediment turbidity (Fig. 4a). Constant low-algae conditions produced fish that averaged 38 mm in length and that did not make the ontogenetic shift until approximately 100 days posthatch (Fig. 4a). Cohorts modeled with continuous high-algae conditions averaged only 24 mm in length, and these individuals generally never achieved the size associated with the ontogenetic shift (Fig. 4a). The algal cohorts also had significantly increased starvation mortality when compared with the sediment cohorts. Individuals in low-algae conditions experienced nearly 80% mortality, and those in high-algae conditions experienced over 99% mortality owing to starvation (Fig. 4b). Because survival was very poor in the high algae conditions, additional runs were completed to improve the sample size of survivors to estimate growth.

Using the relationships observed in the static-condition scenarios, we developed a “best growth” model that would represent growth of yellow perch under ideal turbidity conditions. The best growth model applied high sediment turbidity until the mean cohort length exceeded the threshold to switch to the juvenile feeding regime. Turbidity was then switched to low sediment to maximize juvenile-stage growth through the remaining days. No algal turbidity was applied to this group, as even low levels of algal turbidity reduced growth rates in both developmental stages. The cohorts in this model averaged 96 mm in length at 124 days posthatch, which was approximately 4% larger than the largest observed length (western basin, 1987, 92.4 mm, Fig. 3a).

Our algal turbidity scenarios, which simulated algal blooms lasting for 2, 4, and 8 weeks at the end of the season, produced
reductions in growth of 11%, 23%, and 45.5%, respectively, compared with the best-case scenario (Fig. 5a). Additionally, starvation
mortality increased from <10% in the best growth model to >60% in the 8-week algal bloom treatment (Fig. 5b). A 1-week algal bloom
during the second week of the larval stage produced results similar to a 2-week bloom during the juvenile phase, with a 10%
reduction in mean cohort length (Fig. 5a) and starvation mortality of 19% (Fig. 5b). An algal bloom during the larval phase also delayed the ontogenetic shift in these cohorts by approximately 12 days (Fig. 5a).

Our IBM showed that prolonged sediment turbidity after the ontogenetic shift had less severe effects than algal turbidity but still produced reductions in growth and increases in starvation mortality when compared with the best growth model. The 2-week
extension of high-sediment conditions produced only a 3% reduction in mean cohort length at 124 days posthatch (Fig. 6a) and a 2%
increase in starvation mortality (Fig. 6b). The 4-week extension of high-sediment conditions produced a 12.5% reduction in growth
(Fig. 6a) and a 22% increase in starvation mortality (Fig. 6b); these results are similar to those obtained with a 2-week algal bloom
late in the season (Figs. 5a and 5b). The 8-week sediment turbidity treatment resulted in a 26% reduction in mean cohort length
(Fig. 6a) and a 28% increase in starvation mortality (Fig. 6b)."

What I hadn't considered prior to diving into this topic, is that turbidity from one cause does not have the same impact as turbidity from another cause. In other words, algal turbidity vs sediment turbidity impact the environment in distinct ways.

It makes sense at face value to fertilize in order to feed the lowest elements of the food chain, therefore I was surprised to see that algal turbidity led to as much as 45.5% reduction in growth and mortality was above 60% when compared to their "best growth" model that started with high sediment turbidity then changed to low sediment turbidity, with ZERO algal turbidity. Even low levels of algal turbidity resulted in 80% mortality and high algal turbidity led to 99% mortality.

What isn't clear (pardon the pun) is how this translates to other species.

What led me to dive into this topic is evaluating the turbidity and staining of my pond water. My next quest may be to dive into how stained (but otherwise clear) waters impact the aquatic environment. The waters around me are the color of ice tea; clear but brown stained from tannins (predominantly from Eastern Hemlock I presume). Although Secchi disc readings are often one foot or less, brook trout thrive.

Thanks for sending the Secchi disc vs NTU charts. I looked for quite awhile without success.