If we place a semipermeable membrane (like that in a reverse osmosis filter) between sealed bodies of salt water and fresh water, the fresh water will gradually travel through the filter by osmosis.

如果我们把一个半透膜(如，在反渗透过滤器)之间的海水和淡水密封机构，将逐步淡水通过渗透穿过过滤器。

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Such an alteration would be needed to allow freshwater fish eggs to survive and travel far in salt water.

ECONOMIST: Fish genetics

Ms Bell said while grey seals do travel upriver, their bodies are adapted to salt water conditions.

BBC: Grey seal spotted in Bewdley and Stourport-on-Severn