The Rideau Valley Conservation Authority has issued a flood warning for communities in low-lying areas along the Rideau River.
Up to 50 millimetres of rain is expected to fall over the area from overnight Wednesday to Friday morning.
The combination of heavy rain, the spring snowmelt, and already high water levels puts flood-prone areas at risk.
One of the areas identified in the RVCA news release is the stretch of the Rideau known as the Long Reach between Kemptville and Kars, including Hilly Lane, Cedar Beach, Rideau Glen, Fairmile, Greenline, Lorne Bridge and other low-lying neighbourhoods.
Another area at risk is in Old Ottawa South including Rideau River Drive at Belmont Avenue, as well as sections of Windsor Park and further north at Brantwood Park.
Flooding could begin by midday Thursday and peak by Friday night or early Saturday.
On Tuesday the Mississippi Valley Conservation Authority issued a flood watch for Dalhousie Lake and smaller creeks and tributaries.
The Ottawa River Regulation Planning Board has also released a statement informing residents in low-lying areas along the shores of the Ottawa River between Ottawa and Montreal of the possibility of minor flooding in the next few days.
The City of Ottawa is providing free sand and sandbags 24/7 at its Hurdman Yard compound at 29 Hurdman Road.
Residents are also reminded that higher water levels can have an impact on areas away from the river as well, including open water, ditches, ravines, culverts, and even outdoor wading pools, which might collect water that cannot drain properly.