What are algae and algal blooms?

Algae are tiny microscopic plants that grow naturally in lakes. An algal bloom is a dense concentration of the plants. Algal blooms generally occur under high nutrient concentrations when one species of algae out competes other algae and becomes so abundant that the water appears murky.

Most blooms in New Hampshire are made up of either diatoms or blue-green algae. Diatom blooms usually occur in the late spring or early summer and are less objectionable than blue-green blooms. Diatoms turn the water a bright green or brown, but do not create the scums and odors associated with blue-green algal blooms. Diatom blooms often occur without being noticed by lake users. Blue-green algae blooms create a greater problem for lake users because blue-greens are subject to concentration by wind action and to scum formation at the surface of the lake. This scum may be blown into the shallows and onto exposed rocks, making the shoreline appear to be covered with blue-green paint. When these algae die and decompose, the resulting odor can be very unpleasant.

What Can Be Done? - Treatment Options.

An algal bloom is an indication that a problem exists within the watershed. These primitive plants are receiving so many nutrients that they are reproducing in vast quantities, impairing the aesthetic quality of a pond or lake. The only complete solution is to locate the source of nutrients and reduce their availability to the pond or lake. This can be successfully achieved but considerable money and time is required to accomplish such a task.

If the algae is not a toxin emitter, the algicide copper sulfate may be utilized to kill the bloom. However, it must be stressed that this is only a temporary solution. Before copper sulfate is applied, a permit must be obtained from the N.H. Pesticide Control Board and a licensed applicator must administer the algicide.