The low flows are straining supplies for farmers, reservoir operators and endangered fish from the mountains to the Utah-Colorado border. Farmers, fruit growers and other water users in Mesa County have some of the oldest, and therefore most secure, water rights in the state. Even with these powerful water rights, farmers in the Grand Valley are facing water restrictions, according to the Grand Valley Water Users Association. And the water users association isn’t even tapping the maximum amount of water allowed under its water rights. Then there are the upstream reservoirs, which also play a role in how water flows down the Colorado River.