Native fish species in the San Juan River reproduce during high spring runoff events, which historically would overflow the banks of the river and spread out into the riparian zone creating off-channel spawning habitat. Since the completion of Navajo Dam, the portion of the San Juan River between the dam and Farmington became unsuitable for native fish due to the reduction in seasonal fluctuations. However, at Farmington the San Juan is joined by the Animas River – which is not controlled by any major dams – and regains some of its seasonal characteristics. In addition, the impoundment of water at Navajo Dam does not appear to have a significant effect on the amount of sediment transported in the river; thus, the aquatic environment of the lower San Juan, though somewhat degraded, still resembles pre-development conditions.