I had a similar fish kill with oaks. New pond built in fall - 1/2 acre x 10ft deep - builder left all of the oaks in the bottom of the pond. Stocked w/ Bluegill, bass and channel cats. Come July here in Oklahoma of the first year; the pond burped and killed majority of the bass and catfish. When I completely drained the pond an pulled out all of the trees a few years later in attempt to seal it better, I was amazed at the amount of the timber down there!
