Sudden reductions in river flow may cause high mortality of juvenile salmonids through stranding. Much higher incidence of stranding was found in daylight during winter conditions compared to at summer temperatures.

Diving observations and radio telemetry show that juvenile salmon and trout move rapidly into newly water-covered areas when discharge is increasing. Salmon parr does not show more movements during frequent flow variations than for stable conditions. Young brown trout seek cover during frequent and rapid flow changes.

We found no significant increased stress level in young brown trout subject to repeated peaking operations. In rivers with almost daily peaking operations, the distribution and composition of invertebrates and water vegetation are severely disturbed only in the dewatered zones.

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