I have a one acre pond that is 15' at its deepest point. For the past 20+ years, the pond has held crayfish, FHM and Rainbow trout. Other than grass and a few small willows along its banks, to the best of my knowledge, there is no other vegetation in the pond.
During the summer months we have an aerating fountain located in the deep end that is programmed to run for about 8 hours each night when the temperature is coolest. During the winter we have an aerating diffuser installed in the shallow end that is set to run about two hours each day to keep a section of our pond free of ice. The ponds only source of water is rainfall and a small spring.
Last August, for the first time we had a bloom in the pond and the water turned a pea green. You could only see about 6" into the water at its worse. I had hoped that with winter and colder temperatures the pond would clear but as of February 3rd found it to be only slightly clearer with the ability to see maybe a foot or so. I should note that other than the green coloration of the pond water there have been no other changes noted. No floating or submerged vegetation or other material that I have observed. To the best of my knowledge there have been no adverse effects on the trout yet.
I have discussed the issue with my pond supplier that I purchase my trout from and he told me not to worry that he bloom will not hurt the water or the fish.
I am still concerned however. Any information or recommendations would be appreciated

I would think about introducing some smaller feeder fish that may convert that biomass into something that can move up the food chain, like FHM or similar. In the low visibility water, they may stand a chance of survival and reproduction rather than being an expensive snack.

What has changed in the area - fertilization , land plowed or disturbed , spring changes (amount , upstream disruption)? What was once a limiting factor has been removed.

Actually we have a good population of FHM and crawfish in the pond now. Trout is the only predator in the pond and we make sure to limit the total population. The grassy shallow areas are generally teeming with FHM. I was wondering if scuds or fresh water shrimp would be a good addition at this time and would help to clarify the water somewhat.

Nothing has changed to my knowledge. The aerator fountain was out of service for about 10 days last July. However it was put back into service before the bloom developed also this fountain has only been in service for three summers and prior to its installation we never had an issue with a bloom.

I agree with ewest. Something has changed, and it might even be something that you can't see, like more dissolved fertilizer in the incoming water.

The denser the phytoplankton bloom, the higher risk you run of running low on O2 when the sun is absent, either very cloudy days or at night. Anything less than 12" visibility on a secchi disk would raise warning signs to me on making sure the aeration system was running during any period of clouds or at night. At night the lowest O2 levels happen right before sunrise, but I'd play it safe and start aerating when the sun goes down.

SOMETHING had to change recently, or you'd have had this problem way before this.

The only thing that I did differently was to spray some of the willows growing around the edge of the pond with Roundup last summer. I used a hand sprayer in which contained at most one gallon of mixed Roundup/water solution. I was very careful not to get any in the water, however I may have allowed an ounce or two to overspray the willows and enter the pond. Unless some of the Roundup entered the water through the willow roots.

This is a good example of why water/soil tests are a good idea. If you had a before and now water test results you could compare and see what has changed.


How many/much willow coverage is involved? Willows at the waters edge can use up some (but not large amounts) of fertility from the water. Their death would leave more fertility in the water to grow plankton. I don't think that would cause large changes however.

Are you feeding your fish? Increased nitrogen and phophorous from the feed can cause blooms, especially with other sources of nutrients present.

I have a small automatic feeder and averaged feeding one 20 lb. bag of Blue Seal floating fish food every two weeks. In most years, feeding generally begins in early April at ice out and extends thru Mid-late November. I stocked 100 Rainbow Trout in the pond in late October and observed them chasing FHM in the murky water during a warm spell in December just before the pond surface entirely froze.

I wasn't even aware that you could have pond water samples tested. Are the results similar to soil tests that list such things as pH, P, K and Ca in mg/l. Do any test labs advertise these services on Pond Boss?
The willows that were sprayed are all smaller bushes which have just sprung up within the past five years. Most are less than six feet tall with the largest being about twelve feet. I was originally going to allow the willows to grow to provide cover for the FHM and crayfish but they have started to take over the shoreline in places.

Correct, I don't know if this test will copy/paste here or not.

Nope, it won't. Even more detailed than a basic soil test. Cost more though!

Here's what we test for:
NH3 CL S04 NO2 NO3 SIO2 SRP TP TKN COND SS

pH you do at the pond and can use the test strips for an aquarium or a swimming pool.

See this from the archives.

http://forums.pondboss.com/ubbthreads.php?ubb=showflat&Number=113216#Post113216

Wow! thanks ewest, it looks like I have some reading to do.
I have also started to keep a "Pond Log" to document all of my pond happenings and observations.

Hey Ken havnt seen a thread called "Kens pond log" yet. I always like reading about other peoples finds.

Yea, I hadn't even thought about posting a "Kens Pond log" on the Forum, most of it would be way too boring. Something to think about though!

I was able to get back to my pond on 3/09/20. I found it ice covered with the exception of an approx. 50' circle of open water above the diffuser. I did see some live and a few dead FHM along with a dead floating trout. I was able to take some water quality tests with my newly purchased water testing kit.

Here are the results: pH between 6.0 and 6.5, NH3 close to 0.0, Nitrite close to 0.0, Phosphate between 0.0 and 0.25,

The water still has a green coloration with a water clarity of 18" by secchi disk.