These are lakes that have weed killer sprayed on them four times a summer and the locals also put a ton of fertilizer on their lawns. The good weeds are gone and the algae are thick. Seems like a contributing factor at least.
Snail also has two deep holes and a lot of shallow water. Once the oxygen goes in the small hole and you are in trouble. I’d also expect Silver lake in the eastern metro to have a similar fate. Very shallow with only one deep hole.