Summer Algal Blooms

A natural occurrence in all surface water supplies, an "algal bloom," is responsible for taste and odor changes in the treated drinking water supply. Algal blooms usually occur in Lavon Lake, the water supply for the City of Terrell, in late July and into August each year, but can occur at any time (summer or winter) if the right conditions exist in the water supply reservoir.

What conditions cause algal blooms in Lavon Lake?

Nutrients must be present - such as nitrogen, phosphorus, and calcium, which are derived from decaying vegetation in the lake.

Turbidity has lessened - the turbidity or cloudiness of the lake water has cleared up, allowing the penetration of the sunlight. This occurs due to lack of rainfall.

Temperature increase - the optimum temperature range of the lake water for an algal bloom to occur is between 80° - 85°. This is provided through many hot summer days.

When all conditions are met, photosynthesis will take place and the algae will grow and/or proliferate. Algal species, such as anabaena, secrete an "oily" substance from their cells that causes an odor in the water supply. Aquatic fungi, actinomycetes, grow on dead and decaying algae and cause an earthy taste in the water.