Dead fish

[NCYankee]

I went fishing yesterday at a state park near my house. The park has three small lakes. The one I fished is about 20 acres. I fished from one end of the lake to the next from the bank and caught nothing. The weather was warm and the sky was Carolina blue, so I figured I wouldn't catch much but at least a couple. I was moving in the direction of the wind. When I got to the side the wind was blowing to, I saw at least forty dead panfish (sunfish, crappie, etc.) floating on the water or just on shore over about a 100 ft. stretch. I immediately called the local park office. Since it was after 5pm, the park employee I spoke to said someone would be out today to take a water sample. The park officials recently lowered the lake a few feet. I'm guessing the lake is probably only 12 ft. deep at the deepest point at full level. The park employee suggested the oxygen levels were probably low because of them lowering the water. She thinks that may be the reason for the dead fish. This could in part explain why I didn't catch anything. Any biologists out there? Is this a reasonable explanation as to why the fish died and others weren't biting?