The water is exposed to sunlight, which increases ‘the rate of photosynthesis, and consequently there is great biological productivity. Where the water is slow, rooted seed plants grow in streams.
In general the difference between streams and ponds revolve around a triad of conditions:
(a) Current is much more of a major controlling and limiting factor in streams.
(b) Land-water exchange is relatively more extensive in streams.
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(c) Oxygen tension is generally more uniform in streams and there is no thermal or chemical stratification.
The algae of running water have received much less attention. Four groups of algae are found frequently in the streams and river, i.e., cyanophyta, chlorophyta, euglenophyta and encrusting pacillariophyta. The first important groups of associations are those of the microscopic, unicellular, collonial cyanophyta forms.