Most of the other rivers and streams inhabited by the wild brown trout are rough, boulder-strewn torrents that drain regions dominated by high moor and mountain. After heavy rain, the huge volume of water draining through the steep slopes of the uplands will cause the river to rise rapidly. During periods of drought, these rivers shrink to mere trickles, exposing large banks of bare gravel. In the heat of the summer sun, or in winter weather, these banks may almost be sterilized of animal life. West Allen River is a typical upland spate stream.
Brown trout can often cope with such extremes of water flow.
In droughts, when the river is low, they may become nocturnal in habit. They will seek the cool still pools beneath the shade of overhanging trees, or the aerated pools beneath waterfalls. Then, come sunset, they will move into the shallows to feed. When the river is in spate the trout will seek the quieter corners, often amongst flooded bankside vegetation, where the flow is less. Spate streams produce relatively little food, so the trout grow slowly.