Algae of many varieties are naturally present in the reservoir and can experience increased growth from time to time. When sunlight, water temperature, and nutrient conditions are optimal, blue-green algae blooms can reproduce rapidly in fresh water. Additionally, the reduced water volume in Fontenelle Reservoir due to below average inflows from reduced snow pack last winter has further facilitated the algae growth.

Tests at Fontenelle Reservoir are underway to evaluate the extent of certain blue-green algae species known to release toxins potentially harmful to humans and animals. Once the water temperature drops in the reservoir in the coming weeks, the subsequent algae die-off will reduce the odor and unusual water color. If these algae have produced toxins, it will take several weeks following the die-off before the water quality will improve as the toxins dissipate. Meantime, while Reclamation continues testing water samples in the reservoir and in the river below the dam, minimized contact with the water in the reservoir by people and animals is recommended.

Fontenelle Reservoir is owned and operated by Reclamation, and the DEQ's Water Quality Division has oversight responsibility for pollution control and watershed management in the state of Wyoming. The recreational areas at Fontenelle are co-managed by Reclamation and the Bureau of Land Management.