Clear Lake will undergo a major transformation in the next few weeks as the weeds start to die off and the algae disappears. This has been the third year in a row that the weeds and algae have just about taken over the lake and while it isn”t quite as bad as some of the previous years, the weeds and algae have had an impact on the tourists and others who use the lake.
Aquatic weeds are much like their land-based cousins. Their purpose is to bloom, spread their seeds and then die. Most of the weeds in the lake have completed their blooming cycle and are nearing the end of their life. In fact, in many areas the weeds have already began to die off.
As the weeds die off and decompose they use up oxygen in the water. Oxygen in the water is made up of gaseous bubbles and is called dissolved oxygen or DO. Oxygen is a vital component of life for both humans and animals, including all species of fish. Humans and other animals receive theirs through their lungs. The lungs take in the oxygen and distribute it to the blood, which is then carried throughout the body.
Fish receive their oxygen through their gills. The gills are made up of a series of small membranes containing a rich supply of blood. This is often apparent to fishermen when they deep-hook a fish and it bleeds profusely around the mouth. What has happened is that the filament in the gills has been either cut or torn.
A fish breathes by opening its mouth and inhaling the water through its gills, which extract oxygen molecules (DO) from the water and then transfer them to the blood vessels. In other words, gills serve the same purpose for fish as lungs do for humans.
Dissolved oxygen (DO) is created by wind, current and wave action, which mixes the oxygen from the air with water molecules. Aquatic plants also furnish oxygen through a photosynthesis process. DO is rated in milligrams per liter — the higher the number, the more oxygen in the water.
Trout, salmon and other cold water fish require a DO reading of at least 8. Bass, bluegill and crappie need a reading of at least 5 to be comfortable. At Clear Lake the highest the DO levels normally get during the summer months is 7. When the DO drops below 5 the bass either vacate the area or become lethargic. If it drops too low the larger fish will leave but often the minnows stay and die.
DO is always lowest at night because the plants aren”t growing and don”t produce oxygen. Actually, the plants will use up oxygen at night. Warm water normally has a lower DO reading than does cold water.
The other major factor going on right now is that as these aquatic plants die and decompose they use up a lot of oxygen. The commercial herbicide companies that spray on the lake to control the weeds are required to take DO readings in the area they plan on spraying because they will be killing a lot of aquatic plants. If the readings are too low they have to delay their spraying.
DO levels also vary from the surface to the bottom. Normally the DO levels are higher at the surface because of wave action, which stirs up the water. This is similar to an aerator that is used in aquariums. Bass fishermen have long known how important oxygen levels are on the behavior of the fish. In fact, some of the more experienced fishermen even carry DO meters so that they can monitor the levels and seek out the areas that show a rich oxygen content.
The other good news for lake users is that the algae is rapidly disappearing. There are days when the algae blooms but the cool nights keep thick blooms down and by mid-September the algae should be just a memory. Of course, next summer the weeds and algae will be back. It”s all part of the normal cycle at Clear Lake.
