Dozens of fish died after rising temperatures reduced the amount of oxygen in a pond.
About 50 fish died in the Leam at Friday Bridge, on Saturday morning as temperatures soared following a warm summer week.
Fire and rescue crews were called to help oxygenate the pond, before Environment Agency officials came to help.
A spokesman for Cambridgeshire Fire and Rescue said: “The high temperatures last week caused a pond in The Leam, Friday Bridge to warm up, decreasing the amount of oxygen available to resident fish.
“Around 50 fish are thought to have died, so a crew from Wisbech used hoses to re-circulate and agitate the water - allowing the water to become re-oxygenated.”
A spokesman for the Environment Agency said:” Officers went to The Leam, Friday Bridge, on Saturday morning and dosed the pond with 100 litres of hydrogen peroxide to help raise the oxygen levels in the water.
“A few dead fish were observed and those that were alive weren’t gasping, but looked a bit listless and the introduction of the hydrogen peroxide had an immediate positive effect.
“Oxygen levels in water can deplete when warmer weather causes the water temperature to rise and we have seen this happen in a few places in Lincolnshire, and this area in Cambridgeshire.”
Residents are asked to keep an eye out over the summer for any waterways or ponds where numbers of fish are struggling, or have died.
If you have any concerns about sightings of dead fish or fish in distress call the Environment Agency incident hotline on 0800 80 70 60.