Flood Watch - Mattawa River downstream of Hurdman Dam

Message Number: 2025-11

Issued: May 13, 2025 at 11:30 AM EDT

From: NBMCA Duty Officer, Angela Mills

FLOOD WATCH notifies that the potential for flooding exists within specific watercourses and municipalities. Municipalities, emergency services and individual landowners in flood-prone areas should prepare.

If you have a flood emergency, please contact your municipality. If you live in an unincorporated township, please contact the Ministry of Natural Resources (MNR) – North Bay District. For Flood Messages related to the Ottawa River, please refer to the MNR North Bay District.

A FLOOD WATCH remains in effect for the Mattawa River, downstream of Hurdman Dam to the Ottawa River.

This is an update to the previous Message Number 2025-10 dated May 6, 2025.

Current Conditions:

Water levels on the Ottawa River at Mattawa are high, causing minor flooding in low lying areas along the Mattawa River between Hurdman Dam and the confluence with the Ottawa River. Water from snowmelt and rainfall in the Upper Ottawa River watershed continues to pass through the river system. Water levels in the remainder of the watershed in local rivers have peaked and are near normal for this time of year.

The Mattawa Island Conservation Area is currently experiencing flooding due to high water levels and is closed to the public until further notice.

Current water levels can be viewed by searching Station Names “Ottawa River”, “Mattawa River”, “Chippewa Creek”, “La Vase River”, “Wasi River”, and “Lake Nipissing” at https://wateroffice.ec.gc.ca/search/real_time_e.html

Forecasted Conditions:

Sustained high flows from the Upper Ottawa River watershed will continue to pass through the Mattawa Area. Limited precipitation is forecast for the coming week, with up to 20 mm of rain locally possible Friday (May 16) into Saturday.

The water level of the Ottawa River at Mattawa is forecast remain stable over the next few days and remain high for this time of year, per the Ottawa River Regulating Committee. The Ottawa River water levels are managed by dams and reservoirs operated by provincial and federal governments. The Ottawa River Regulation Planning Board posts current data and forecasts on their website https://ottawariver.ca/

The water level on Lake Nipissing is regulated by dams operated by the federal government. Water levels have reached normal summer navigable water levels. More information is available at https://www.canada.ca/en/public-services-procurement/services/infrastructure-buildings/bridges-docks-dams/frenchriver-dam.html

Historic Flood Conditions:

For comparison, when river-based flooding occurred in Mattawa in May 2019, the water level on the Ottawa River at Mattawa reached a maximum level that is 128 cm higher than the present level. Flows from the Otto Holden dam in May 2019 were around 40% greater at their maximum than present.

Risk:

Water levels remain elevated in the lower reaches of the Mattawa River due to high flows from upstream tributaries to the Ottawa River. Flooding is expected to persist where it is already occurring. A Flood Watch is in effect for the lower reaches of the Mattawa River, downstream of the Hurdman Dam, where water levels are directly affected by high flows on the Ottawa River.

All residents, especially those in low lying areas, are encouraged to monitor the conditions that are developing. Banks adjacent to rivers and creeks are very slippery at this time and when combined with cold open water, pose a serious hazard. The public is encouraged to keep children and pets away from watercourses and waterbodies.

Municipalities are encouraged to monitor water crossings for debris that may affect the movement of water through culverts and bridges. A close watch on local conditions and updated forecasts and warnings from Environment Canada is also recommended.

Staff at the North Bay-Mattawa Conservation Authority will continue to monitor weather and watershed conditions and update this message based on the changing weather and streamflow conditions.

This message will be in effect until (or updated before) Tuesday, May 20, 2025, at 4:00 PM EDT.

The general public is advised of these messages through the www.nbmca.ca website with the flood status icon and a link to information about current conditions. NBMCA also circulates these messages to local media and social media, posting on Twitter (@theNBMCA), Instagram (nbmcainfo), and Facebook (NBMCA).

The public is invited to share photos of watershed conditions on social media using #NBMCAFlood.

Media Release issued May 13, 2025

https://www.nbmca.ca/watershed-management/flood-forecasting/flood-watch-status-terminology/

North Bay-Mattawa Conservation Authority Subwatershed map — *^{NBMCA Subwatershed Map}*

Lake Nipissing

Flows through the dams are based on daily analysis of the current status of the lake and river and as agreed to by the Sturgeon-Nipissing-French-Wanapitei Water Management Group. Weather forecast is considered, along with the inflows from the upper watersheds and outflows through the dam to the French River.

You can view the current level on Lake Nipissing at North Bay on the graph below and the French River at the Water Survey of Canada (WSC) website. Fluctuations in the levels are a result of the strong winds affecting the movement of surface water. Water level and flow information for the South River and Sturgeon River systems is available from Ontario Power Generation (OPG).

Flood warnings for Ontario can be found on the Ontario Flood Forecasting and Warning website.

Why the fluctuation in water level readings on Lake Nipissing? Lake Nipissing can sometimes act like a bathtub, with water shifting in the lake, depending upon wind direction, speed and atmospheric pressure - known as a wind surge or seiche. At times the wind can have such an impact that it may result in the level being higher or lower at the French River gauge compared to the gauge located on the North Bay shoreline.

Mattawa River

The current Ottawa River water level may be viewed at the Water Survey of Canada (WSC) website (note that there is a delay of several hours, and 100m should be added to the gauge reading for metres above sea level).

The Ottawa River Regulation Committee and Ontario Power Generation which operates the Otto Holden Dam provide information online regarding the management of water levels on the Ottawa River. To view water levels and current conditions on the Ottawa River visit the Ottawa River Regulation Planning Board and Ontario Power Generation.

Watercourses and Monitoring throughout the Watershed

There are other watercourses within the NBMCA jurisdiction which are monitored by NBMCA and other agencies. These gauges are maintained by Water Survey Canada - Environment Canada and can be viewed in real-time online.

In addition to the Water Survey of Canada gauges, there are other staff gauges which are monitored by NBMCA or the Ministry of Natural Resources and Forestry: