Historically this has occurred about once every hundred years. In modern times, considerable effort has been made to strengthen levees and control floods. Below is the list of hydroelectric power stations built on the Yellow River, arranged according to the first year of operation (in brackets):   As reported in 2000, the 7 largest hydro power plants (Longyangxia, Lijiaxia, Liujiaxia, Yanguoxia, Bapanxia, Daxia and Qinglongxia) had the total installed capacity of 5,618 MW. The main bridges and ferries by the province names in the order of downstream to upstream are:  Shandong  Shandong–Henan  Henan  Shanxi–Henan  Shaanxi–Henan  Ningxia  Inner Mongolia  Gansu  Qinghai The Yellow River basin is rich in fish, being the home of more than 160 native species in 92 genera and 28 families, including 19 species found nowhere else in the world (endemic). However, due to habitat loss, pollution, introduced species and overfishing many of the natives have declined or disappeared entirely; several are recognized as threatened on China's Red List. Dams and their reservoirs have increased the habitat for species of slow-moving and static waters, while it excluded species of flowing waters and prevented the up- and down-stream breeding migration of others. In the 2000s, only 80 native fish in 63 genera and 18 families were recorded in the Yellow River basin. In contrast, introduced fish have risen in both abundance and number of species; only one introduced fish species was recorded in the 1960s when ichthyologist Li Sizhong published his original survey of fish fauna of the region, but by the 2000s there were 26. As typical of Asian rivers, Cyprinidae is by far the most diverse family in the Yellow River basin. More than 85 cyprinids have been recorded in this basin, including species that still are present and species that no longer are present. Other highly diverse families are the stone loaches (more than 20 species), gobies ( 15 species), true loaches ( 10 species) and bagrid catfish ( 10 species). Although there are species found throughout much of the river, several have a more restricted range. For example, the uppermost, highest parts on the Qinghai–Tibet Plateau has relatively few native species, notably snowtrout and allies ("Gymnocypris", "Gymnodiptychus", "Platypharodon" and "Schizopygopsis"), and "Triplophysa" loaches.