Game and Fish has requested the flushing flow in order to maintain fish spawning habitats and to increase production of invertebrates that fish depend on for food. The Bureau of Reclamation will begin releasing additional water from Gray Reef Reservoir in the early morning hours beginning Monday, March 16. Flows will increase from approximately 500 cubic feet per second (cfs) to 4,000 cfs and will then gradually decrease back to 500 cfs each day, with the maximum flow occurring between 3-9 a.m. The schedule will be repeated through March 25. The flows below Gray Reef Dam will then be stabilized at approximately 500 cfs for the remainder of the month. This schedule may be modified again if river ice conditions persist.
In recent years, flows were increased for 5 days each spring and occasionally repeated for another 5 days in the fall. However, the
fall flush has been problematic in that it dislodges aquatic vegetation and moves it downstream, causing loss of vegetative cover and invertebrates in upstream reaches of the river. A 10-day flush in the spring may be better able to maintain high quality spawning habitat for trout.“Data show these flows are important to trout spawning and to the numbers of trout in the river,” said Matt Hahn, fisheries biologist for the Casper region. In the past, the trout population has fallen to less than 400 trout per mile, even with stocking. Since annual flushing flows began in 1995, the trout population averages over 3,500 per mile and stocking has been eliminated upstream of Casper.
The Game and Fish Department advises sportsmen and recreationists to be aware of the potential dangers related to flushing flows. Because the flush will span the weekend, there is potential for more people to be wading or floating the river. Those using the river during the flushing flow should consider the fluctuating water levels and be aware that areas that can be waded effectively at 500 cfs may not be safe at 4,000 cfs.
Biologists will be collecting spawning habitat data pre-flush, after five cycles, and post-flush. The data will be used to evaluate the value of five and 10 cycles to determine if the additional cycles provide additional benefits.
Flushing flows are normally scheduled for completion in March to avoid any impacts to spawning rainbow trout.