Why do fish kills happen during summer?

Answer 1

How Summerkill Occurs

Excessive Vegetation Scenario—Many Ohio ponds become "choked" with vegetation during July and August. Fortunately, excessive vegetation by itself will not cause a fish kill as the high amount of oxygen produced during daylight easily compensates for respiration and decomposition. Problems can arise during a hot, calm, and cloudy weather pattern. A substantial reduction in sunlight causes the amount of oxygen produced to decline while oxygen consumption remains unchanged. Thus, oxygen levels slowly decline. Ponds can usually withstand several consecutive cloudy days but if clouds persist for longer periods, oxygen levels may decline to levels harmful to fish life, about 3­4 ppm for largemouth bass and bluegills. A fish kill due to insufficient oxygen may begin to occur, particularly just before sunrise when daily oxygen levels are at their lowest. The first fish to die are the larger individuals as their oxygen needs are greater. Fortunately, a sunny day will quickly raise oxygen levels and end the fish kill. A common result of this scenario is a partial fish kill which leaves the pond's fish community dominated by small fish.

Late-Summer Herbicide Treatment—Many owners prefer to have minimal vegetation but wait until the pond has become choked with plants before initiating any control measures. This can lead to a serious oxygen problem if all the vegetation is treated simultaneously with an herbicide/algaecide. Soon after treatment, a massive die-off of the treated vegetation will occur. The actual timing of the die-off depends on the herbicide used and other conditions. But once die-off begins, it proceeds rapidly. This causes a substantial build-up of organic material that begins to decay in the warm water, and which requires large amounts of oxygen to complete. Coinciding with the die-off is a decline in oxygen production as the plants responsible for that production are now lying dead on the pond bottom. Oxygen consumption far outpaces oxygen production and levels begin to decline significantly. Couple this situation with a calm, cloudy day or two, and a fish kill can occur.

Premature Fall Turnover—Any pond that stratifies during summer will undergo a normal fall turnover as water temperatures decline. This process is described in Ohio State University Extension Fact Sheet A-7-01, Understanding Pond Stratification. A fish kill can result in some ponds that experience a premature turnover in late summer.

http://ohioline.osu.edu/a-fact/0008.html

Answer 2

I am assuming you mean due to temperature...

During the summer a lake would have several different temperatures of water inside it. This is called the temperature gradient. Water is at it's densest at 4 degrees, meaning that this water will be at the bottom. But the lake must be deep enough to allow the water to cool to this temperature.

If during the summer, water levels become low, cooler temperatures can not be achieved and the fish will have no place to cool their body temperatures.

Additional the amount of dissolved oxygen in the lake will vary with temperatures. This is called the Oxygen gradient. Warmer water carries less Oxygen, so if the water is too warm, the fish can't get enough oxygen.

Answer 3

Oxygen (a gas) dissolves more readily in cold water than in warm water. During the summer, when water is warmer, there is less dissolved oxygen. Absent other outside factors, this lower amount of dissolved oxygen can cause fish kills.

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Answer 4

during summer, there is a reduce in the water level of waterbodies. due to this decrease, it is not able to cope up with the excessive amounts of pesticides and insecticides flowing up to the bodies.
hence fish kills happen during sumer.

Answer 5

Reduced water levels, reduced oxygen in water, pollution, infiltration of plants harmful to fish, water temperature to high to sustain fish....