The one constant on Bobs lake is that the water level is constantly changing. Bobs and Crow lakes are reservoirs for the Rideau Canal system and the release of this water through the Bolingbroke dam at the north end of Bobs lake is the sole responsibility of Parks Canada.
Historically the discussion of water levels has been ongoing for a very long time. In 1982 Parks Canada prepared the Rideau Canal Management Plan. The plan used 40 years of extensive data from precipitation to lake evaporation rates to design a comprehensive scientific approach to managing water levels. The resulting 'Rule Curve" shown below, is used on reservoir lakes such as Bobs Lake to determine the best water level throughout the year to support the Rideau Canal. Parks Canada adheres to, given normal events and consistent operations to this Rule Curve.
The Rule Curve model says that the difference in water levels (i.e. The difference between the high water and low water levels) on Bobs and Crow should reach an approximate average of 1.7 m (4 ft 9 in) each year. This is calculated as 1.7 cm per day drawdown over a 100-day period from late June to mid-October (i.e. 100 times 1.7 cm/day = 1.7 m/yr). Over this 100-day time period the Rideau Canal, is continuously fed by the Tay Watershed until approximately the first Tuesday after Thanksgiving in October. This average of 1.7 m is based on a range. This means that in some years it can be higher (e.g., 2.0 m in 2014) and lower in other years.
The Rule Curve does NOT specify the actual water level at any given location on the lake. It only refers to a difference in water levels. This means that in drought years, water levels will be lower. The water level for shallow areas of Bobs Lake may actually recede completely or recede much earlier in the season. Having inadequate direct water access and excessive flooding for a cottage owner are serious issues. However, Parks Canada is entrusted with managing the very delicate balance between cottage owner enjoyment, commercial and tourist requirements of the Rideau Canal and wildlife/fishery habitat needs.