Walkers, joggers and cyclists are being urged to limit use of towpaths after images appeared of people apparently not sticking to social distancing rules at the weekend.
The Canal & River Trust has repeated its advice to follow Government guidance and keep use of the waterways to a minimum, after already putting up thousands of posters along towpaths.
It comes after footage and photos were posted on Twitter showing dozens of people crowding the paths along the Regent's Canal towpath in Victoria Park, Hackney, during the mild weather.
One resident, an NHS midwife at a London hospital who lives on a boat moored by the towpath, posted images of people crowding the narrow footway.
She said the towpath had been particularly busy because of the closure of parks and the sunny weather.
She called for towpaths to be used only for essential travel such as to and from work, better, larger signage such as that seen on the Underground and more police patrols.
Two Met Police motorcycle outriders did turn up after she reported what was happening.
Victoria Park was closed at the end of March by Tower Hamlets Council, after what it called the failure of some visitors to stick to social distancing.
She said another neighbour, an NHS doctor, recorded 600 people passing their boat in the space of an hour.
Health Secretary Matt Hancock has warned outdoor exercise could be banned if people continued to flout rules.
It comes as the Canal & River Trust, which oversees 2,000 miles of waterways, has released a new poster urging people to limit towpath use.