Water Safety Statement - North Bay-Mattawa Watershed

Message Number: 2025-07

Issued: April 17, 2025, at 1:30 PM EDT

From: NBMCA Duty Officer, Githan Kattera

Watershed Conditions Statement – Flood Outlook gives early notice of the potential for flooding based on weather forecasts calling for heavy rain, snow melt, high wind or other conditions that could lead to high runoff, cause ice jams, lakeshore flooding or erosion.

Watershed Conditions Statement – Water Safety indicates that high flows, unsafe banks, melting ice or other factors could be dangerous for users such as anglers, boaters, swimmers, children, or pets. Flooding is not expected.

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.

A Watershed Conditions Statement – Flood Outlook has been issued for the inland rivers within the North Bay-Mattawa Watershed.

A Watershed Conditions Statement – Water Safety has been issued for the Lake Nipissing Shoreline in the City of North Bay and Municipality of Callander and the lower reaches of the Mattawa River through the Town of Mattawa.

Current Conditions:

Water levels on area lakes and rivers are normal for this time of year, and area lakes remain ice-covered. As of April 15, the average moisture content in the snowpack is 26.3 mm, which is typical for mid-April. Snow persists in higher elevations, while forested areas show patchy coverage. Soils may still be frozen in some locations or have recently thawed and are near saturation, limiting their ability to absorb rainfall and snowmelt.

Water levels for Lake Nipissing and the Ottawa River at Mattawa remain within normal ranges for this time of year and are well below flood thresholds.

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:

Temperatures are forecast to be approaching 10 ºC during the day and near freezing overnight over the coming week with approximately 15 to 25 mm of rain forecast on Friday (April 18) and an additional 10 mm Monday (April 21). Water levels and flows are expected to increase in response to the rainfall and melt of remaining snowpack.

Water levels on the Ottawa River are managed by upstream dams and reservoirs operated by provincial and federal governments. Forecasts are available at https://ottawariver.ca/

The water level on Lake Nipissing is regulated by dams operated by the federal government. Forecasts are available at https://www.canada.ca/en/public-services-procurement/services/infrastructure-buildings/bridges-docks-dams/frenchriver-dam.html

Historic Flood Conditions:

For comparison, in response to 34.5 mm of steady rain over 12 hours with frozen or saturated soil conditions and minimal remaining snowpack in March 2024, the water level on Chippewa Creek increased by 83 cm over 15 hours, peaking about 3 hours after rain ended.

Risk:

Forecasted mild daytime temperatures and rainfall, combined with continued snowmelt will increase runoff and raising water levels across the watershed. A Flood Outlook is in effect for inland rivers, as there is a risk of flooding in low-lying and flood-prone areas. Rainfall on frozen or saturated ground may cause rapid changes in water levels, particularly along urban creeks in the City of North Bay, during and after intense rainfall.

Increasing water levels and runoff are expected to impact shoreline ice stability. A Watershed Conditions Statement – Water Safety is in effect for the Lake Nipissing Shoreline and lower reaches of the Mattawa River in Mattawa, as fluctuating water levels and ice breakup are a hazard but water levels in these areas are well below flood thresholds and flooding is not expected in these areas.

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 off 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) Friday, April 25, 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 April 17, 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: