为了更好的对河流水体污染进行控制和治理，及时了解河流的水质状况是必要的。
To better control and prevent water pollution in rivers, it is necessary to know the conditions of water quality in rivers in time.
河流水体受污染后，在自然环境因素的影响下由各种物理、化学及生物作用能得到一定的净化。
When river water body is polluted, it can be purified by kinds of physical, chemical and biologic functions under natural environment factors.
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