A lake was a large body of fresh water. Lakes were common on class M planets.
Betazed had two notable lakes, Lake El'nar and Lake Cataria. (TNG: "Dark Page", "All Good Things...")
Balfour Lake was a body of water located on an unnamed planet. (TNG: "Attached")
Lake Tahoe was one of the largest freshwater lakes in the western United States of America. It was located near Reno, Nevada, where it shared a border with the state of California. (DS9: "It's Only a Paper Moon"; VOY: "Vis à Vis") Lakes George and Como were also located on Earth, the latter being in Northern Italy. (VOY: "Coda", "The Swarm")
The Lake of Lusor was a body of water located on Qo'noS, the Klingon homeworld, near the Kri'stak volcano. (TNG: "Rightful Heir")
Lake Yuron was one of the few bodies of water on the planet Vulcan. (VOY: "The Disease")
In 2377, four holographic Starfleet officers, including Weiss, hid in a lake during a hunt on a Hirogen training facility. As two Hirogen approached, they emerged and shot them with their phaser rifles. (VOY: "Flesh and Blood")
The Axiana Lakes, on the planet Talaxia, were several large bodies of water connected to each other and were located near the Godo Mountain Range. (VOY: "Homestead")
Lake Armstrong was a large artificial body of water on Earth's moon, which, on a clear day, could be seen from Earth itself. (Star Trek: First Contact)
A large lake existed on the Ba'ku planet and was home to at least one species of fish. In 2375, Lieutenant Commander Data uncovered a cloaked Federation holoship hiding on the lake. (Star Trek: Insurrection)
In 2399, Jean-Luc Picard conversed with William T. Riker on the pier of a lake on the planet Nepenthe. (PIC: "Nepenthe")
In a deleted scene from TOS: "The Immunity Syndrome", Leonard McCoy claimed to have lived near a lake as a child. He tells Christine Chapel a story about falling through a hole in the ice and being unable to find the place where he fell in. Someone who he still does not know the identity of to this day pulled him out. He then relates his having wanted desperately to see daylight again with the absence of stars created by the space amoeba's appetite. (Star Trek: Lost Scenes)