Clear Lake will see a major transformation in the next few weeks as the massive weed beds die off. Because of the lower-than- normal rainfall and runoff into the lake this year, the aquatic weeds literally exploded. Many fishermen told me they had never seen the weeds extend so far out into the lake. In some areas, the weeds stretched nearly to the middle of the lake.
Aquatic weeds, like all plants, only serve one purpose and that is to bloom, spread their seeds and then die. The various species of weeds have completed their blooming cycle and are now nearing the end of their life. The massive die-off will have a minor impact on the lake and the fish. As the plants die and decompose, they use up oxygen in the water. Oxygen in the water is made up of molecules. It”s called dissolved oxygen or DO.
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 made up of a series of small membranes that allow blood to flow through them. The water that passes through the gills contains oxygen molecules. These membranes extract the oxygen from the water and transfer it to the blood, the same as the lungs do for mammals. Dissolved oxygen consists of microscopic gaseous bubbles that are suspended in water. This is the actual oxygen a fish uses.
Dissolved oxygen is formed by wind and wave action that stirs up the water and allows oxygen to mix with the water. Aquatic plants also furnish oxygen through a photosynthesis process.
DO is rated in milligrams per liter. The higher the number the more oxygen is in the water. Trout and other cold-water fish require a DO reading of at least 8. Bass need no less than 5 to be comfortable. Late in the summer in some of the channels on Clear Lake the DO readings can be as low as 2 or 3. When DO levels drop the fish respond by either moving out into water with higher DO levels or sometimes they just become lethargic and don”t feed or do very little swimming.
There are a number of factors that affect the amount of DO in a body of water. DO levels are lowest at night because the plants don”t grow in the dark and don”t produce oxygen through photosynthesis. In fact, at night these plants actually use up the oxygen. Water temperature also plays a role. When the water is cold it holds more DO than when it”s warm.
During the late summer and fall months the decaying plants also use up a lot of oxygen. As the plants die and decompose, the water often turns a dark brown or even black color. Most experienced fishermen will look for water that”s a green color because they know it has a higher oxygen level.
There is no question that DO readings are important to fishermen. If you knew the DO in an area, you would know if fish are there. If you were fishing in one of the canals and the DO was low, then chances are that the bass have temporarily moved out of the area and you would be wasting your time. A few fishermen even carry DO meters that measure the oxygen levels in the water.
The optimum level for bass is 7-9, but in Clear Lake it”s rare to find a DO level higher than 8 during the summer and fall months.
DO levels also vary from the bottom to the top of the lake. Normally DO levels are higher near the surface because of wave action stirring up the water and creating oxygen, much as the aerator does in your aquarium at home.
By October most of the aquatic weeds will be gone and the water will begin to clear up. Hopefully there will be enough rainfall this winter to bring the lake level back to normal. The one sure thing is next summer will see a return of the weeds because the lake is now clearer than any time in history, which makes ideal growing conditions for the weeds.
