Fish kills can occur when oxygen levels in water drop sharply. This happens when algae consume dissolved oxygen overnight, after producing it during the day. The Texas Parks and Wildlife Department says stormwater runoff can contribute to this process by carrying extra nutrients into waterways.

Low wind and water flow can also cause problems, leading to layers of water with different oxygen levels. This can affect fish that gather in areas with low oxygen. Further information about a recent incident is available from the Texas Parks and Wildlife Department, which investigated a large number of dead fish found in a waterway.