Passive coal mine water treatment schemes in the United Kingdom typically incorporate settlement lagoons to precipitate iron and collect HFO (hydrous ferric oxide). Laminar flow in the lagoons enables HFO particles to settle out under gravity. Preferential flow paths through the lagoon can have a detrimental effect on treatment efficiency due to short circuiting. A field trial was undertaken at the operational Clough Foot mine water treatment scheme, Yorkshire, to assess the impact of incorporating baffles within an existing operational lagoon. Baffle curtain installation was predicted to improve lagoon hydraulics and enhance treatment performance by creating flow paths to reduce short circuiting of mine water within the lagoon.