Environmental hazards induced by humans also puts sirenians at risk. Sirenians, especially the West Indian manatee, face high mortality from watercraft collision, and about half of all West Indian manatee deaths are caused by watercraft collisions. An increased usage of hydroelectric power and subsequent damming of rivers increase waterway traffic, which can lead to vessel collisions, and manatees may become entangled in navigational locks. The urbanized coastline of areas such as the Caribbean and Australia can result in the decline of seagrass populations. Reliable areas of warm water in Florida are generally the result of discharge from power plants, but newer plants with more efficient cooling systems may disrupt the pattern of warm water refuges, and an increased demand for artesian springs for water, the natural source of warm water, decreases the number of warm water refuges. Sirenians can be caught as bycatch from fisheries, and they can be seen as pests with the interference of local fishermen and the destruction of their nets. African manatees have also been known to venture into rice paddies and destroy the crops during the rainy season, and these confrontations with locals may lead to intentional culling of the manatees.