The submerged vegetation of Lake Pontchartrain, in southeast Louisiana, was surveyed before and after the April 1973 opening of the Bonnet Carre’ Spillway. Abundant species were Vallisneria americana Michaux., Ruppia maritima L., and Najas guadalupensis (Sprengel) Magnus. Potamogeton perfoliatus L. was recorded only near Point aux Herbes and Zannichellia palustris L. only in North Pass. Floating and nonrooted submerged species were noted throughout the lake but were not recorded at each survey area. The study revealed approximately 2,000 acres of waterbottom covered with submerged vegetation, the greater portion of which was recorded between Green Point near Mandeville, and Big Point near Slidell, along the northeastern shoreline of the lake. In general, similar abundance values were recorded in both surveys for submerged vegetation along the northeast shoreline. The release of fresh river water did not have observable effects on the submerged vegetation.