With the hot weather, aquatic weeds and thick algae, a number of people are wondering how all this will impact the fish in Clear Lake. The massive algae blooms in the south end of the lake could have an impact by using up the available oxygen in the water. In the north end the weeds that extend out into the middle of the lake have not only scattered the bass, but later this summer, when the weeds start to die off, the oxygen levels could also drop.
Fish, like humans, require food, habitat and oxygen to survive. The food and habitat are in the lake, but what about sufficient oxygen? Whereas humans get their oxygen from the air around us, fish get theirs from the water. It”s called dissolved oxygen (DO). DO is measured in milligrams per liter. The higher the milligrams per liter, the more oxygen in the water. DO levels can range from one to 18. Trout and other coldwater fish require a DO reading of at least eight. Bass need no less than five to be comfortable. When the DO drops below five, some fish will die and if it drops below three, just about all the fish will die.
Oxygen enters the water through aeration, such as when the wind ripples the water or there is water movement. Dissolved oxygen is formed by wind and wave action that stirs up the water and allows oxygen to mix with the water which forms gaseous molecules. This is why home aquariums have pumps. Aquatic plants also supply oxygen to the water by a method called photosynthesis. Plants generate oxygen during the day, but use up oxygen at night. Plants also use up oxygen when they die and decompose. This decomposing results in bacteria, which uses up the DO.
DO is also lower in warm lakes than in cold lakes. Clear Lake is a huge shallow lake and during the hottest days of the summer the water temperatures can be as high as 90 degrees. This hot weather can deplete the available oxygen in the water. Oxygen is a vital component of life. Be it human, animal or fish. Animals receive their oxygen through their lungs. However, fish receive their oxygen through their gills. The gills are actually a series of small membranes which the blood flows through. The water that passes through the gills contains oxygen molecules. The gills are membranes that extract the oxygen from the water and transfer it to the blood, the same as the lungs do for animals. Dissolved oxygen is microscopic gaseous bubbles that are suspended in water. This is the actual oxygen a fish uses. Fish use up more oxygen when the water is warm that when it”s cold because as the water warms up their body metabolism increases.
Fish react to low oxygen levels in several ways. The adult fish will either slow down their activity, which uses less oxygen, or move out into water that has more oxygen. If they can”t find water with sufficient oxygen they can die. This occurs more with juvenile fish because they don”t know enough to leave an oxygen starved area. In the past there have been die-offs of fish at Clear Lake during the late summer months. Especially in some of the channels because the oxygen levels tend to decrease in these areas because of a lack of wind action and water movement.
This year the thick algae blooms in the south end of the lake could result in low DO readings, especially at night. I remember 15 years ago when I accompanied a fishery biologist to the Clearlake Oaks Keys during the massive algae blooms. We measured the DO levels several times during a 24-hour period. The levels were as low as three, just at daylight and as high as six by mid-afternoon. The areas we measured also had very few fish.
There have been a lot of ideas on getting rid of the algae and weeds, but the reality is that Clear Lake is such a large lake there are very few solutions. Algae has been part of Clear Lake for hundreds of years. In 1872, Dr. Livingston Stone (a world renown scientist) visited Clear Lake and wrote in his journal that during the month of August the algae was so thick that he couldn”t push his boat through it.
The bottom line is that Clear Lake will always have algae and aquatic weeds. Some years it will be thick, such as this year, and other years there will be few weeds or algae. It”s part of the nature of the oldest lake in North America.
