About 70% of the wetlands surrounding Upper Klamath Lake have been impounded and drained, eliminating much of the habitat used by juvenile suckers during their development. Healthy wetlands also absorb contaminants such as phosphorus, which in excessive amounts causes blooms of organisms, especially the cyanobacterium "Aphanizomenon flos-aquae". These blooms have led to sucker die-offs because the blooms deplete the dissolved oxygen in the water. The water quality in Upper Klamath Lake is poor, especially during the summer. While the sucker is relatively tolerant of poor water quality, compared to other fish, there is a history of multiple sucker die-offs.