Why are estuaries particularly vulnerable to the effects of pollution?

Estuaries are especially vulnerable to pollution because they are at the end of all the pollution from factories and farmland runoff all the way down the river. Rivers have been used as rubbish dumps all through history, and this is still happening in many places. Estuaries that do not get a good flushing out by the sea tides are especially vulnerable.

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D. peatlands,grassland,swamps