section_path: Conservation/Other threats
section_name: Other threats
paragraph_text: Other threats
  
  A key stress on both freshwater and marine ecosystems is habitat degradation including water pollution, the building of dams, removal of water for use by humans, and the introduction of exotic species including predators. Freshwater fish, especially if endemic to a region (occurring nowhere else), may be threatened with extinction for all these reasons, as is the case for three of Spain's ten endemic freshwater fishes. River dams, especially major schemes like the Kariba Dam (Zambezi river) and the Aswan Dam (River Nile) on rivers with economically important fisheries, have caused large reductions in fish catch. Industrial bottom trawling can damage seabed habitats, as has occurred on the Georges Bank in the North Atlantic. Introduction of aquatic invasive species is widespread. It modifies ecosystems, causing biodiversity loss, and can harm fisheries. Harmful species include fish but are not limited to them; the arrival of a comb jelly in the Black Sea damaged the anchovy fishery there. The opening of the Suez Canal in 1869 made possible Lessepsian migration, facilitating the arrival of hundreds of Indo-Pacific marine species of fish, algae and invertebrates in the Mediterranean Sea, deeply impacting its overall biodiversity and ecology. The predatory Nile perch was deliberately introduced to Lake Victoria in the 1960s as a commercial and sports fish. The lake had high biodiversity, with some 500 endemic species of cichlid fish. It drastically altered the lake's ecology, and simplified the fishery from multi-species to just three: the Nile perch, the silver cyprinid, and another introduced fish, the Nile tilapia. The haplochromine cichlid populations have collapsed.