Without a question, the topic across Nebraska is the hot dry summer.
How bad have things been? A north-central Nebraska radio station recently broadcast that there would be no weather report from Wood Lake because “their temperature thingy was broken.” That’s hot. So is this topic: how mid-summer heat affects fish.
We naturally think of water as being cooler than the atmosphere, and we assume fish need that cool environment to survive. That is true for cool-water or cold-water species. A cold-water fish such as rainbow trout cannot survive above a certain temperature. Its biochemistry ceases to function once the water gets too warm. There are temperature limitations in bodies of water in which a given fish species can survive. Stocked rainbow trout cannot survive the summer in a small urban lake in southeast Nebraska, and even a cool-water species such as northern pike has a distribution limited by temperature.
Warm-water species not only tolerate warm-water temperatures, they thrive in them. The hot summer weather does not necessarily pose any danger for these species — as long as these fish have sufficient water and good water quality. Currently, a large stretch of the Platte River in central and east-central Nebraska does not have any water. Fish cannot survive those conditions. During a drought, some river stretches can dry up, and to a certain extent, that is a natural event on the Great Plains. When that happens, those river stretches lose all fish. When the water comes back, the fish come back.
Liquids can hold less of a dissolved gas at higher temperatures. Warm water has less dissolved oxygen capacity than cool or cold water, and there usually is less dissolved oxygen in water during the middle of the summer. Low oxygen levels can cause fish die-offs during the summer in waters that have quality problems.
Excessive nutrient loads in some waters can fuel algae blooms. Algae are microscopic plants, and all plants produce oxygen via photosynthesis. However, when the sun is not shining, plants such as algae respire and consume oxygen. In a small body of water, severe mid-summer algae blooms can result in more than enough dissolved oxygen in the water during the day. However, after dark, toward morning or after a few cloudy, calm days, that algae can use so much oxygen that it causes a fish kill.
Every angler will tell you that fishing success tends to lag during the “dog days” of summer. A popular excuse for not catching fish is that fish become lethargic and uncomfortable during the heat and just do not feel like feeding. That is not true. Fish are poikilotherms. That means that the body temperature of fish is the same as their environment. Fish do not feed less during the summer because they are uncomfortably hot. Their metabolism rates increase with the warmer water temperatures and they actually feed as much or more during the summer than they do in any other season. Even species that are nearing their upper lethal temperature will continue to feed right up to the point when they die.
Fishing gets tough during the middle of the summer because of the abundance of natural prey available to the fish. With warm water temperatures, the entire aquatic food chain is operating at maximum capacity and zooplankton, aquatic insects, small fish and many other organisms are at their peak abundance during the middle of the summer. It is almost so easy to get a meal that all a hungry fish has to do is swim around with its mouth open.