Laguna de Metztitlán. 02/02/04; Hidalgo; 2,937 ha; 20°41'N 098°52'W. Reserva de la Biosfera. A natural dam formed when a limestone landslide blocked the course of the Venados River. It has an average depth of 9 to 10 m, covering 700 ha, yet it may flood 5,000 ha under exceptional conditions. Vegetation types present include montane shrubs, oak-pine forest, deciduous tropical forest, "crasicaule" shrub, desert scrub, Juniperus forest and aquatic vegetation. The lake is a stopover and wintering ground for migratory birds. It feeds aquifers that are tapped for agriculture and which feed the Almolón River springs downstream. The scarce native fish life prompted the introduction of tilapias, carps and catfish, which are harvested and destined forlocal markets. Silting due to erosion in the hillsides and water pollution are generating problems of eutrophication. The use of small-eyed fishing nets also poses problems for sustaining fish stocks. A management plan is in place for the Biosphere Reserve. Ramsar site no. 1337. Most recent RIS information: 2004.