Photo of Zosel Dam

Raising the water level in Lake Osoyoos for spring

OROVILLE March 17, 2015– Dam operators are raising the water level in Lake Osoyoos as spring weather advances in Washington state and the greater Okanagan Valley in Canada.  Local residents should be aware that sudden rises from early snow melt can cause temporary flooding along shoreline properties.

The lake level is managed by the Washington Department of Ecology at Zosel Dam in Oroville to support irrigation and summer recreation in both the United States and Canada. The level of the lake is raised slowly from the winter operating level to the summer level until about June 1.

“Our challenge is to keep lake levels from rising too quickly during this period,” said Al Josephy, with Ecology’s Office of Columbia River. “This time of year we must coordinate lake levels with other lake management operations in Canada as well as respond to snow melt and rain or snow events."

Ecology’s target is to maintain a level between 911.5 and 912 feet from May 1 to Sept. 15.

Lake levels are mandated by the International Joint Commission, a board made up of representatives from the United States and Canada. For more information on the operation of Zosel Dam or Lake Osoyoos, contact Al Josephy at 360-407-6456.

To track lake levels in “real time,” as well as find additional information, go to the U.S. Geological Survey web page for Osoyoos Lake.

Brief Chronology of Zosel Dam's History - 09/25/2001 International Joint Commission

Osoyoos Lake Water Quality Society - Dams and the Okanogan River

Lake Osoyoos Board of Control

Streamflow and Weather Data Sources

USGS Washington Water Science Center 

Water Office Canada Real-time Hydrometric Data

National Weather Service

Osoyoos Lake International Water Control Structure - Zosel Dam

Zosel Dam, the dam in the U.S. that currently maintains Osoyoos Lake levels, was initially built in 1926 by William Zosel. Mr. Zosel owned a sawmill along the Okanogan River in the town of Oroville, WA, and needed a millpond for the storage of sawmill logs.  Mr. Zosel received the necessary permissions to build the dam, but it appears that no consideration was given at the time to potential impacts of the dam on Osoyoos Lake levels in Canada.  Operation of the dam at this time caused fluctuations in lake levels and lakeshore flooding.

By the early 1940s, local residents complained about lake conditions to the International Joint Commission (IJC), which had been created as a result of the Boundary Waters Treaty of 1909 to adjudicate transboundary water-body disputes.  In 1946, the IJC issued its first Order of Approval for Zosel Dam, which established dam operating requirements.  These Orders have been modified twice since, most recently in 2013.  The Orders largely address lake levels as their main concern.

By the 1970’s this wooden structure had fallen into severe disrepair.  As the Zosel operation had largely abandoned the dam, it fell to the State of Washington to propose a fix to the situation, in order to continue to maintain lake levels at Lake Osoyoos.  Working cooperatively with the Province of British Columbia, a plan was put in place to build a new, all-concrete dam structure.

Project Description:

Construction of Zosel Dam was completed in April 1987 at Oroville.  The site of the new dam is two miles downstream from the Osoyoos Lake outlet and nine miles south of the United States/Canadian border.  The Department of Ecology owns this structure for the State, but the local irrigation district, Oroville Tonasket maintains the site and structure for the State.

To improve channel capacity, dredging was completed upstream from the new dam.  Sand bars that partially blocked the channel at the Osoyoos Lake outlet were removed.  Also, sedimentation buildup at the confluence of Tonasket Creek with the Okanogan River was dredged.  Channel improvements were completed in early 1988.  The State continues to monitor channel conditions on a regular basis as part of the Orders of Control.

Improvements were also made at the Osoyoos Lake State Park.  A sheet pile wall was installed along 600 feet of the west bank of the state park to improve bank stability along the Osoyoos Lake outlet.  A new boat launch, sidewalk, handrail, and rock fill-groin at the beach were included in the project.

In the News

Water level lowered at Osoyoos Lake for the winter - Ecology News Release - November 5, 2014

Help for thousands of salmon on incredible journey from Oregon to Canada - ECOconnect Blog July 28, 2014

Lake Osoyoos rises as runoff increases Washington operations help maintain lake levels for many uses - Ecology News Release May 29, 2014

Ecology makes seasonal water level changes at Osoyoos Lake - Ecology News Release September 19, 2013

Water levels rise at Lake Osoyoos as temps rise - Ecology News Release May 7, 2013

IJC issues Order for future management of Osoyoos Lake water levels International Joint Commission (IJC) January 31, 2013

U.S., Canada, Washington State agree to new cross-border lake operations  - Ecology News Release January 14, 2013

Ecology makes seasonal water level changes at Osoyoos Lake - Ecology News Release November 8, 2012

Water Levels are rising at Lake Osoyoos - Ecology News Release May 24, 2011


Al Josephy
Department of Ecology - WR
Phone: 360 407-6456