Coral reefs are particularly vulnerable to sedimentation, siltation, and eutrophication processes. Soil erosion from upland deforestation exacerbated the problem of siltation downstream and into the sea. Erosion, siltation of drainage networks and flooding result. Slowed net siltation and erosion result in net reduction in sediment transport. It has been extirpated in areas with excess turbidity and siltation in western Ohio. They are intolerant of pollution, turbidity and siltation, and require a minimum pH 6.0. Sand siltation required dredging, which weakened the quays; one quay collapsed in 1924. Urbanization often leads to the siltation of sandy beaches, decreasing their viability. Also, changes in flow regime and siltation of spawning habitats may reduce recruitment. Overall, these reservoirs suffer from rapid siltation. The lake is shrinking rapidly due to siltation and lack of inflow. The lake has become shallow due to siltation and accumulation of plant debris. Central Taipa is a plain as a result of siltation and land reclamation. They are anadromous spring spawners and prefer clean streams with light flow and light siltation. Originally the seasonal flow entered the lake directly causing heavy siltation.