Question
Two weeks ago after a heavy rain all of the fish in my pond died.  This is not the first time it has happened.  I had stocked it again last year after they had all disappeared.  Recently after a heavy rain all the fish died.  What might cause this?  The pond is spring fed with a bog bottom.  Any information would help.

Thanks

Answer
There could be a number of issues.  First, rain water is often acidic, has no hardness, and is low in oxygen.  So, enough of it could cause a pH drop, hardness drop, or suffocation from lack of oxygen if not well aerated.  The rain changes the pond's water chemistry.  Not only are the actual readings sometimes problematic but any fast drastic change in water chemistry can stress fish.

Then, rain also causes run off into the pond.  If the pond gets runoff from mulch and dirt, there can be an algae bloom.  If gasoline, pesticides, herbicides, etc. get washed in, the fish die.  Does your pond get a lot of runoff?  Where does the runoff come from?  Have you tested the pH, hardness, alkalinity, and oxygen levels when the pond is doing well versus when the fish have died?  How big is the pond?  I hope you can figure it out.

Good luck!

Robyn
fishpondinfo.com