Pond Boss Forums MANAGING AN EXISTING POND Evaluating and adjusting fish populations Winterkill

Scott, looks like you have a similar case to Big Bear Lake (BBL) shallow pond areas, Lake Perris extended flood pond, and two small lake like ponds in the high deserts near our area. Here's the scenario:

1. You utilize an diffuser system within the 3' to 4' feet depth based on wind condition. Fish are now trained to go to the depth that's has the best oxygen supply.

2. As Sue indicated, summer time, oxygen at the bottom, not at the top, were consumed by biological decay (biological oxygen demand - BOD) by bottom dwelling organisms. Rather than fish remained at the bottom depth during winter to keep warm, there is no oxygen at the bottom, so they linger at the surface area, once again, trained earlier by the diffuser. DO at point of water introduction, 0mg/L. Point of DO 6 to 8ft away, 3mg/L.

3. Your soil, with just a quick glance to the best of my knowledge is great for retaining biological decays, as well as encouraged for biological growth due to nutrient retention and water diffusing down and out. Look at the surround tree groves. Beautiful growth during warm seasons.

4. Oxygen from the start was low before introduction of your fish, even though you're monitoring for the DO, which was in a low minimal standards for biological survival rate, especially for HSB. You stopped monitoring the DO, believing that the diffuser would induce enough DO into the water when there's not enough wind to stir up the water to infuse the water with oxygen. Quite few nailed that.

Now, this is the scenario that match the waters' (not so much at the Lake Perris' flood pond) conditions during cold winter when snow arrived and light ice caps were created, with similar to your pond's depths around the edge before the drop off. Rather than BBL shallow areas and ponds having diffusers, they actually have water from the local streams flowing in, or the water from the rain/snow melts flow in. The killer of the trout, carp, and catfish were the ice capped the water from the top, without wind from introducing oxygen into the water. The ice cap also prevent the water from the streams and the surrounding from being introduced into the waters. So, no DO in the waters during cold days.

Now, I'm not sure if your diffuser was running during the cold days, but it appears the fish kept on chasing for DO at the shallow area (trained from earlier) possibly where the diffuser was, since the DO was less than than tolerable DO level for HSB (minimal is 1mg/L). What made me curious is the single trout bellied up, without others being the same, unless you find others later at the bottom when the conditions allow to search. Last desperate chance was to swim to the opening the ice to create enough surface disturbance to create enough DO in the water for survival. Thermal shock between surface water temperature vs lower water temperature would be also an influence of their mortality. We did find fish tried to breath by jumping out of the water, and literally just lied on top of the ice through a small opening, yet, met their dooms.

For the time being, create a plan of approach. Have the diffuser go deeper to prevent the shallow death (I believe there was problem with fish death if diffuser in deep water from posts that I read?), and increase DO at the lower depth as DO migrate to the upper layers of the water during calmed conditions. Your water pressure may not allow you to push the air down that low, but you may have to alter your course of action.

Ensure that diffuser actually either sit on top of a large gravel bed, or sitting under a light gravel bed, to prevent pond organic fine debris from clogging the diffuser. The rock, if layered on top of the diffuser, will also increase the DO stratification in the water column.

I'll await for the sample to come, and I'll let the staff here take a poke at it, and if possible, have them use what we have available in our lab to see what's in the soil during their down time.

Hope I shed some kind of light to the darkness. If anyone see something that I cannot at the time being, please, chime in!