Lac Seul is a large, crescent shaped reservoir in Kenora District, northwestern Ontario, Canada. It is approximately 241 km long. It has a maximum depth of 47.2 m, with a surface elevation of 357 m above sea level. Its level is raised in the summer and then drawn down in the winter months to reach points of as low as 16 feet below the maximum level…Lac Seul is a large, crescent shaped reservoir in Kenora District, northwestern Ontario, Canada. It is approximately 241 km long. It has a maximum depth of 47.2 m, with a surface elevation of 357 m above sea level. Its level is raised in the summer and then drawn down in the winter months to reach points of as low as 16 feet below the maximum level. It is the second largest body of water entirely within the province of Ontario.