The council has started regular seawater sampling, to get a fuller picture of the condition of local waters.
Officers will take regular samples at Southsea, Langstone Harbour and Portsmouth Harbour, to monitor water quality and track any changes.
Cllr Steve Pitt, the council’s Cabinet Member for Culture, Leisure and Economic Development, said: “We’re obviously aware of public concern about seawater quality, especially among swimmers and water sports enthusiasts. We’re in regular contact with Stop the Sewage Southsea and other campaigners.
“We’ve started this sampling programme because we want to reassure residents and visitors that data is being collected and the situation is being monitored.
“This isn’t part of the council’s normal role, but there’s a shortage of comprehensive information and we need to know the full picture. We need to have a clearer idea of what’s happening around our coastline, and this research should give us that.”
The council will initially take samples for a 12-week period, starting this month. It is liaising with the Environment Agency, Havant Borough Council, Langstone Harbour Board, Southern Water and the Southern Water Regional Forum.
Sarah Shreeve, co-founder of Stop the Sewage Southsea, said: “We know that people are keen for water testing they can trust, all through the year, as the residents of the city love using the water all year round. We’re thrilled the council are helping to keep us informed as to the status of the water quality which we care so deeply about.”