High temperatures can wreak havoc in fish ponds warns George Lewis, Extension Fisheries Specialist. Warm water can hold much less dissolved oxygen than cool water. Dry weather also causes some ponds to be lower than normal. The combination can be lethal to creatures that depend on oxygen in the water. The worst days for fish are those that are hot and overcast. Less sunshine means less oxygen from the plants in the water. Nightfall exacerbates their distress. For this reason, the best time to check for oxygen depletion is at dawn. If fish are observed “gulping” at the pond surface at dawn, another cloudy day could lead to a large fish kill by evening.
Lewis advises anyone who manages a pond to have an emergency plan for low oxygen levels. Pumps or farm mowers can be used to spray water in the air so it holds more oxygen. Chemicals can be added to increase oxygen levels too. For more information on pond management, call your local Extension office (1-800-ASKUGA-1).