Submerged Aquatic Plants in a Primary Settling Reservoir

September 1955, when a primary settling reservoir in the Cincinnati Water Purification Plant was being drained for cleaning, extensive growths of a grass-like plant were revealed (Fig. 1). A similar growth was found in a second primary settling reservoir drained in September 1956. The first reservoir had a capacity of 180 mil gal, the second, 200 mil gal. Draining and cleaning are carried out at 4-year intervals.