More than 1,000 fish had to be rescued from a weir due to the low flow of water.
Officers from the Environment Agency came to the aid of the creatures in the River Stour, which runs through Nayland.
Areas of the river had dried out due to the recent hot weather, combined with the previous dry winter.
This creates little pools of water where fish can collect but as fresh water cannot get to them, there is little oxygen in it for fish to breath.
The Environment Agency has also identified a stretch of the river 400m upstream where there are another three or four pools where fish could become trapped.
A spokesman for the Environment Agency said: "On Wednesday, August 14 the Environment Agency rescued more than 1,000 fish from a horseshoe weir in Nayland.
"The fish had become trapped in the weir due to low flows.
"We moved the fish upstream and pumped water into the weir pools to help alleviate the flow."
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