Severe environmental stressors are the most frequent causes of sudden fish death in garden ponds or other fish habitats, and the lack of oxygen in the water is the number 1 stressor of all.

Two major factors contributing to fish-pond oxygen loss concern blooming algae. During daylight hours, algae make oxygen; during the night,however, the plants take oxygen. If algae are profusely blooming, the plants deplete all the pond