Several smaller streams, including Stony, Stewart, and Fisher Creeks in the south, Mud Creek in the west and Cain's Creek to the north, also flow into Black Lake. These rivers and streams deliver great quantities of dark tannin-stained waters that give the lake its name.

While "Black Lake" is a common name for many bodies of water, the most famous "dark" lake is Loch Ness in Scotland, and the reason for its inky appearance is the high concentration of peat in the surrounding soil. As rainwater runs down the Scottish hills and into the loch, it picks up particles of decaying organic matter (peat), which stay suspended in the water. This creates a "tea-like" staining effect so intense that sunlight and even powerful floodlights can barely penetrate more than a few feet below the surface. This extreme lack of visibility—often called "murky" or "pitch black"—is what has fueled the legend of the Loch Ness Monster for centuries, as anything swimming more than five feet deep is essentially invisible to observers above. In 2026, researchers continue to study how this peat content affects the loch's unique ecosystem, noting that the darkness provides a perfect hiding spot for large aquatic life and contributes to the loch's "mysterious" and often intimidating reputation among divers and tourists.