Lake Marion is located in a native forest catchment north of Lake Sumner, in the Hurunui – Waiau Water Management Zone. Despite Lake Marion being a relatively undisturbed natural lake, it often has somewhat high concentrations of nutrients. This may be linked to organic inputs from surrounding forest, as well as water remaining in the small catchment for a long time and encouraging nutrient recycling.
The lake is drained by the Marion Stream, which flows to Lake Sumner. The lake is free from introduced fish, and protected as a ‘Faunal Reserve’ (www.ecan.govt.nz).