San Diego & SoCal Fishing Forums

Went out tonight to fish a little, walk around and see a bunch of shad die off. Temp here is around 70 during the day but decreased to north 40 at night. This is my first time seeing a lot of them die off like this. What gives?

Could be low oxygen levels. An algae bloom can result in an algae die off at night and consequent low oxygen levels. Lakes that get run off from fertilized areas (lawns and agriculture) are prone to algae blooms.

40F water temperatures can cause shad die off but water temperatures change a lot more slowly than air temperatures.

Pollution from things like insecticides and weedkiller could be the cause. There was a big fish die off from unknown causes (at least no causes were publicly announced) at Upper Otay years ago. It still hasn't recovered.