Lake Rowallan is a Hydro Tasmania impoundment situated in the upper reaches of the Mersey River Valley in northwest Tasmania, approximately 25 kilometres south of Liena. It is the first of two hydro impoundments constructed on the Mersey River and forms part of the broader Mersey-Forth catchment system. The lake sits at coordinates 41°46′48″S 146°11′60″E. Access from Deloraine involves taking the B12 past Mole Creek, turning left onto the C138, then continuing on the C171 past Lake Parangana. The final few kilometres of road to the lake are unsealed.

The primary boat launch is a well-signposted gravel ramp on the northeastern side of the lake near the dam wall, though it can become difficult or unusable during periods of low water. Four-wheel-drive vehicle tracks also lead to sheltered areas around the lake where small boats can be launched directly from shore. Water levels fluctuate regularly due to the lake's role in hydropower generation, and current lake level information is available from Hydro Tasmania's website. Paddlers should be aware that significant submerged timber exists throughout the lake, posing a genuine hazard to watercraft, particularly propeller-driven boats but relevant to paddlers as well.

From the dam wall at the northern end, the lake extends in a westerly direction. Navigating toward the upper end requires passing through the old river bed, where submerged and partially exposed timber is present. When water levels are high, this section is more manageable, though tree tops may still protrude from the surface. The upper reaches of the lake open out considerably, offering more expansive water.

The lake supports populations of brown trout, rainbow trout, climbing galaxias, spotted galaxias, and river blackfish. There are no formal facilities beyond the boat ramp — no toilets are provided, and campers are required to bring a chemical or portable toilet. The lake is described as a popular family fishing and camping destination. Nearby points of interest include the Mersey White Water Forest Reserve and access routes into the Walls of Jerusalem National Park. Shooting is prohibited in the area, and visitors are required to keep to formed tracks and respect private land boundaries.