Pond Boss Forums INTRO Questions & Observations Need advice on pond, and dying fish, Please

Hi. Im new to this Forum and hope im not breaking any rules by posting here. Im a new pond owner in Manitoba, Canada.. My pond is a natural, half acre pond that I pumped out, and dug the center out, down to 16 ft. So its a natural pond, with a quick drop in the middle. I have an Aeration system going on a frame thats suspended 3 feet above the bottom of the pond. Half of the paremeter is a wheat field and the other half is my yard. But there is a healthy 20 ft border of cattails all around as a buffer. This Spring i put in 300 rainbow trout fingerlings, and this last week, after a particular hot week I found 30 of them floating on the surface within 24 hours, and have since then not seen a single fish feed whatsoever. And the past week has been cool. The surface temp of the water was 70f, but has since cooled off. Please give me some information. Is it possible I still have alive fish left? If not.. what did I do wrong?.. Please ask any question, and I'll do my best to answer. Thankyou kindly

Welcome to the forum!

Rainbow Trout will die once the water temps hit 70°F. There is not enough O2 in the water at that temp for them to live. I have seen trout live in warmer water, but there was a bottom diffusion aeration system that was slightly overkill for the pond running 24/7 AND a surface agitator running 24/7. The O2 levels in the pond were high enough to allow the trout to live until the water hit 80°F. It was super saturated with O2.

The only way to tell for sure is have an O2 meter to test the water, but they aren't cheap. Down here we look at Trout as seasonal stocking, typically going in during late October and getting fished out by late May or late June, depending on how hot the temps were in the Spring. (Northern Indiana)

Hey Essup. Thanks for the welcome!..

My thinking, and hope was that even if the surface water was 70f, the bottom would stay cool enough for them to suvive. i have an Airpump feeding two airdiffuser rocks with a 1.5 inch hose, running 24/7 i thought that was substantial, but i guess not.
Another concern I have is that over 50 of the pond; the shallower parts are covered in aquatic plants, with most coming to the surface of the water, or just underneath.. would those help, or hinder O2 levels?..

Around here we're able to keep some for several years. We put them in as fingerlings, and catch them over 20inches .. we need to resupply the stock every year though, as letting them reproduce is not legal.

With the aeration system running in the deepest part of the pond, the water temp will be pretty much homogenized top to bottom. The plants hinder the pond at night, but help the pond during the day. Without sunlight the plants consume O2 (night time). The most critical time for a pond's O2 level is the last hour of the night into the first hour of day.