Levels of E. coli in the River Stour have been reported to be "alarmingly" high, amid high temperatures this August.
Many people have been enjoying swims during a scorching hot summer in Dorset, but the safety of the water is currently a concern.
Martin Stewart, Chairman of Christchurch Harbour and Marine Society (CHAMS), has conducted tests in the River Stour for E. coli, a type of bacteria that can sit in contaminated water after it has been exposed to sewage.
His tests showed more than 130,000 colony-forming units (CFU's) per 100ml of water in the Stour on Saturday, August 15.
He warns that anything over 1000 is not safe for bathing. On Wednesday, August 19 the tests showed 370,000 CFU's per 100ml, which he called "alarming".
Stewart told the Echo: "I've been having notifications from people who have been ill swimming at Avon Beach, and it's coming from the rivers. It flows straight out.
"50 years ago, any excess sewage went out to Poole Bay. It doesn't do that anymore, it goes into the Stour. That is the big problem that Christchurch Harbour has.
"Christchurch Rowing Club had to row through raw sewage this morning."
He is waiting to see if the Environment Agency (EA) can verify the data, as they are carrying out tests and investigating now.
The CHAMS chair notes that levels "peaked nearly a week ago", but Stewart said: "I’m not blaming the EA for anything. They’ve not been given the funds they require".
Stewart added: "We’ve got our data, we’re very confident in our data. We’ve been collecting it for a long time. We've got no reason to doubt it.
"There's pushback [from Wessex Water] every time one of these events happens".
A Wessex Water spokesperson said: “There have been no recent storm overflow operations at or upstream of that location and all our sewerage assets are operating as normal.
“Christchurch Harbour is a catchment serving a largely rural area where water quality can be influenced by wildlife, agricultural run-off, private sewage sources and numerous other factors.
“Environment Agency data does not identify discharges from water industry assets as the reason for the harbour not achieving a higher ecological status.”
The Bournemouth Christchurch and Poole Council has arranged a public meeting at The Regent Centre at 6pm on September 1 regarding this issue.
The Echo contacted the Environment Agency for more information, but it had not replied at the time of going to print.
