HOOVER, Ala. (AP) — Hundreds of dead fish have been found on top of a pond in Alabama and officials say it appears low oxygen levels are to blame.

Southern Pond Management said shad were the only fish impacted by low oxygen levels in the Lake Crest Pond in Hoover on Tuesday.

Oxygen levels can be reduced when the weather is stagnant, without thunderstorms or heavy rains.

The homeowners association tells news outlets it’s the second fish kill in the pond in two weeks. Test results on the oxygen levels are not back yet.

Scott Sherones with Southern Pond says the problems are worst between June and August.