We have some rivers with riches of nutorients in the water.
Fish grow bigger, but usually environment is not very good...
決して清流とはいえませんが、昔から富栄養の川では魚のサイズが軒並み大きくなります。
周囲の環境には目をつぶって大物狙い・・となると、やはり夕まづめあたりが良さそうですね。

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