Trata-se do inventário floristico da família Scenedesmaceae do lago Água Preta, parte do complexo de abastecimento de água do município de Belém, PA, efetuado a partir de quatro coletas, no período de outubro de 1992 a agosto de 1993. Os resultados mostraram que a família Scenedesmaceae está representada por 15 táxons: Crucigenia fenestrata Schimidle, C. quadrata Morren, Dicloster acuatus Jao, Wei & Hu, Dimorphococcus lunatus Braun, Scenedesmus acuminatus (Lagerheim) Chodat var. acuminatus, S. acuminatus (Lagerheim) Chodat var. bernardii (G.M. Smith) Dedussenko, S. armatus Chodat var. bicaudatus (Guglielmetti) Chodat, S. indicus Philipose, S. perforatus Lemmermann var. perforatus, S. quadricauda (Turpin) Brébisson var. quadricauda, Scenedesmus sp., Tetrallantos lagerheimii Teiling, Tetrastrum heteracanthum (Nordstedt) Chodat, T. punctatum (Schimidle) Ahlstrom & Tiffany e Westella botryoides (W. West) De Wildeman.<br>An inventory of the Scenedesmaceae was made in lake Água Preta. This lake is the main component of the water reservoir of Belém, in Pará State. The inventory was based on four samples collected, during one year, from October 1992 to August 1993. The Scenedesmaceae family is represented by 15 taxa: Crucigenia fenestrata Schimidle, C. quadrata Morren, Dicloster acuatus Jao, Wei & Hu, Dimorphococcus lunatus Braun, Scenedesmus acuminatus (Lagerheim) Chodat var. acuminatus, S. acuminatus (Lagerheim) Chodat var. bernardii (G.M. Smith) Dedussenko, S. armatus Chodat var. bicaudatus (Guglielmetti) Chodat, S. indicus Philipose, S. perforatus Lemmermann var. perforatus, S. quadricauda (Turpin) Brébisson var. quadricauda, Scenedesmus sp., Tetrallantos lagerheimii Teiling, Tetrastrum heteracanthum (Nordstedt) Chodat, T. punctatum (Schimidle) Ahlstrom & Tiffany and Westella botryoides (W. West) De Wildeman.