There is no resident fish population in the monument. Occasionally, when Chicken Creek flows, one or two species may briefly enter the monument from downstream sources.
In 2003, the National Park Service and Wyoming Game and Fish Department conducted an informal fish survey near the confluence of Chicken Creek with Twin Creek, just outside the monument boundary. Twin Creek produced seven native species including redside shiner (Richardsonius balteatus), speckled dace (Rhinichthys osculus), longnose dace (Rhinichthys cataractae), leatherside chub (Gila copei), bluehead sucker (Catostomus discobolus), mountain sucker (Pantosteus clarki), and mottled sculpin (Cottus bairdi). A non-native white sucker (Catostomus commersoni) was also captured.