I’ve recently read on the University of Oklahoma and Mississippi State websites, that they do not recommend swimming in a pond that’s being fertilized.
Does anyone know the reasoning behind this advice? I’m wondering is they believe the fertilizer could be harmful or maybe that it’s not attractive for some folks to swim in heavy plankton. I keep my visibility readings in the 20-22” range so plankton isn’t too thick.
I have a 5 acre pond in SW MS that I’ve fertilized since it was built in 2014 and we swim regularly.
As always, responses and info are very much appreciated. I searched a few times for this subject and didn’t find anything, but I apologize if it’s been covered previously.
Thanks!
Ronnie
Pond Boss Subscriber Since 2014
Without reading the articles, I would bet that they are staying on the safe side of pond swimming advice. In some areas, Blue Green algae gets established all by itself without fertilization. I can only assume that fertilization increases it's likelihood.
I agree with Quarter Acre. Cyanobacteria (blue green algae) is more likely to proliferate with fertilization. Cyanobacteria produce cyanotoxins which have been linked to several health issues. Note, if you do fertilize your pond and create cyanobacteria, the cyanotoxins do accumulate in the fish that feed off them.
Considering fertilization and ponds with green water, you should be most concerned when the surface as thin green or blueish green films on the surface that distribute and move with wind. Most all the cyanotoxin producing algae form surface films. However not all green surface films are caused by Cyanobacteria and sometimes a specie will form toxins and sometimes not. Current consensus is toxin production has to do with the amount of nitrate nitrogen in the water. To complicate things, there are a few genera of toxin producing Cyanobacteria (bluegreens) that are truly planktonic and thrive in the water column and do not form surface films. However not all green surface films are caused by Cyanobacteria. The general rule is to be cautious when green surface films are present.
Fertilizer is not the problem. Nutrients may be the problem. All ponds are different. Some have high natural fertility with out any fertilizer. Others have little fertility even with fertilization. Pond fertilizer generally should have no to little N in the mix (example NPK 0-46-0). High N levels can be a problem with or without fertilizer and high P levels can favor some bad plankton/algae.
See these for more info. But note they are written for raising fish (culture).
https://srac.tamu.edu/serveFactSheet/207https://srac.tamu.edu/serveFactSheet/300 Can you give us the source documents for your concern?
Maybe they are talking about natural fertilizers? High e-coli values=bad swimming?
Nice article. It has to be read very carefully. It is cutting edge but something 99% of pond owners can't do (effectively manage the N/P ratio to produce optimum good plankton blooms).
The reason pond fertilizers are high in P and not N is based on years of water chemistry science and reality. Most non-productive ponds (those that need added fertility) have low to no P and it is the limiting nutrient factor. Without adding P no or minimal blooms will occur. Just like with alkalinity (low alkalinity = no bloom) as alkalinity is the limiting factor. You can add all the N and/or P you want and still not get a bloom.
What is needed is the right ratio of N & P and good alkalinity plus the right plankton species present. In providing advice I try to never let perfect be the enemy of improving the existing situation. The question here is - if you have non/minimally productive waters (no/low plankton bloom) do you accept the situation or try to improve things using available tools ? Learning to make optimal use (not no use) of the tools is what Dave's article is about.
Excellent information guys, thank you once again! I feel like I should mail ya’ll a check or something???)))
I’ve only seen the surface type of blue green algae twice in my pond and it was very minimal, and the water generally appears “healthy” the vast majority of the time. We will continue swimming while keeping an eye out for any of the above concerns.
Thanks much!!
Ronnie
I got a full body rash from swimmers itch after working in my pond trying to pull out watershield. I don't fertilize but the pond seems to stay naturally fertile with about 2ft of visability.