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Jonsson, N. (1991). Influence of water flow, temperature and light on fish migration in rivers. Nordic Journal of Freshwater Research. 66:20-35.

Water flow, water temperature and light are environmental variables that influence when fish migrate and the intensity of the migration itself. These variables apply both to up- and downstream migration, but their effects may among rivers and species. During the ontogeny, migratory fish in different life history stages are transported downstream by the water flow. Changes in water flow may influence when the fish migrate. To be carried downstream, the fish must position themselves within the water column and actively swim of out sloughs and backwaters. High water discharge may stimulate the river ascent. Water temperature is an important factor initiating up- and downstream migrations of several fish species. In particular, this may be the case in rivers where freshets do not regularly occur at the time when the environmental shift is favourable. Migrations of juveniles and adults are mainly nocturnal, but sometimes diurnal. When the migration occurs during dark hours this is expected to be an adaptation to avoid visual predators.