There has been concern recently about fish kills in some of our ponds which was brought to the attention of Pond Professionals, LLC, the company we have under contract to service our ponds. The following communication by their Biologist, George Colbath, explains the situation and will hopefully help our residents understand some of the challenges of balancing the ecology:
The vegetation “killed” was nuisance water lettuce that flushed in from ditches and wetlands with the rain events. This is a noxious weed and had to be eradicated. The few dead fish we picked up and water sample taken reflected an elevated amount of ammonia. This is indicative of the non-native tilapia in that pond being overpopulated. Incidentally, that is the ONLY species of fish picked up on that pond. The rapid decay of the water lettuce after treatment likely caused a temporary dissolved oxygen depletion on the pond as well, that allowed for the weaker fish to die off, exacerbated by their overpopulation. The higher levels of ammonia from too many fish in such a shallow and small acreage promoted rapid growth of the nuisance weeds and algae. I would also like to add that water lettuce has a rapid rate of growth (exponentially over 48-72 hours). It is imperative we address water lettuce as soon as possible due to this rapid growth rate. The dissolved oxygen levels have returned to normal.
While it can be alarming seeing a fish kill event, in the case of Tilapia it is an unfortunate but natural occurrence within storm water ponds on occasion. This is due to the shallow design, minimal water body connectivity and the species rapid reproduction rate and the minimal amount of native game fish available to control the population. This seems to be returning to normal at this time. This winter, as things slow down and the weather cools, I would suggest having us take some water sampling from the ponds that are experiencing abnormal algae growth this year to check the ammonia levels. We can then start scheduling some selective netting to remove the tilapia and allow the water chemistry to balance itself. Aquatic plants are a large aid in this. A good way to follow what we mean is to visualize any koi pond you may have seen before. They are always dirty, very green and turbid because they always have way too many fish. This is due to the elevated ammonia levels. Spore algae and most aquatic plants thrive on this ammonia by product from the fish.
Another solution we recommend that would allow us better access to the stormwater ponds and to improve overall aesthetics is to gain access all the way around each pond by clearing the overgrown easements. Many of them have lost access to large portions of the ponds and allowed brazilian pepper trees to overhang and “seed” the water column with high nutrient berries etc.
I hope this helps shed some light on things. For the homeowner’s peace of mind, all of our staff are licensed with the State of Florida and all products used are industry standard for storm-water use and what is labeled, recommended and applied according to the EPA and Florida Department of Environmental Protection. No pesticides nor aerosol products are used in or around the ponds.