Long-term decisions of where to manage the lake level are based on water level controls across the seasons. Let it get high over winter when it is wetter and let it drop over summer to keep the rivers flowing even when there isn't much rain.

Short-term decisions about how much to release and at what time on a given day are based on water levels and electric power needs. If the lake is higher than they want it to be for that time of year, they will release more. If it's lower than they want it to be for that time of the year, they will release less. If it's summer, they will release what they have allocated for that day in the afternoon/evening when power demands are highest. If it's winter, they will release in the morning because power demands are highest then.

Yes, they also consider impacts on both the fishery and recreational uses of the reservoirs and rivers, but it's primarily based on flood control and power generation needs.

Hope this helps.