Two terrapins were scooped from stagnant ditches in Dartford earlier this month as part of a six-day rescue mission.
Rare breeds expert Wayne May was called out to the industrial estate in Sandpit Road, Northfleet, by an ornithologist who spotted the animals in distress while monitoring bird activity.
Mr May recruited a team of volunteers who spent days in waders and surgical gloves, searching with nets in the 2ft-deep mud for the terrapins, thought to be abandoned pets.
The 42-year-old, who runs an animal sanctuary in Dartford, said: "The ditches there are so polluted. It was dire.
"Without a doubt they were abandoned pets.
"They were in a ditch and covered in polystyrene all over them and the water was all stagnant.
"There is no way they could have survived the summer given the environment they were in."
Mr May believed there could have been more in the ditches but the team was unable to find them.
He said: "We cleaned the two we found with cold water and a toothbrush, covered in green slimy algae, their shells are stained.
"It’s a real tragedy to see animals abandoned like that.
"Now they have to spend six months in quarantine."
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