A part of the Saint Lawrence River drainage basin, the lake has the highest altitude of any body of water within the Rideau Canal system.

The bedrock in the Precambrian landscape consists mostly of gneiss and marble and is covered in a very thin layer of mixed glacial sediment.

The southern half of Upper Rideau Lake is located between the Algonquin Highlands and the Smiths Falls Limestone Plain.

The bedrock here consists of Paleozoic quartzose sandstone, dolomite, and conglomerate covered in a variety of sediments: glacial till, silt, clay, organic deposits, and sand.

It was originally intended to remain one lake when an attempt was made to excavate the naturally rocky shallows on the Upper Narrows.

Colonel John By finalized plans to build a dam and a Narrows Lock, separating the waters and forming Upper Rideau Lake.

The Water levels of the Rideau Canal system are monitored by the Ministry of Natural Resources and Forestry and Parks Canada.

Water levels are managed for recreation, allowing for drafts during the navigation season and for residents with docks, boathouses, and shorefronts.

Upper Rideau Lake has large populations of bass and other fish, making it a popular spot for recreational fishermen.

[4] The Foley Mountain Conservation Area, located on the banks of the lake near Westport, is a small park containing 5.5 miles (9 km) of hiking trails.

The most commonly observed mammals include squirrels, chipmunks, coyotes, foxes, porcupines, skunks, beavers, otters, muskrats, mink, raccoons, and white-tailed deer.

[10] In 2018, the Village of Westport completed a Large Subsurface Disposal System (LSSDS) costing roughly $3,000,000 to treat the sewage.