Lake Iso-Melkutin is a clear-water freshwater lake in Loppi, southern Finland, known among divers and freedivers for its visibility and varied underwater terrain with submerged ridges, trees, and rock formations that suit cold-water and under-ice freediving. The lake supports views of small fish such as perch and ruffe around 4–7 m depths and offers opportunities for snorkelling, scuba diving, and ice freediving retreats in winter. Nearby activities include hiking around the lake and using saunas or lakeside facilities coordinated by local organizers or freediving groups. Local dive and freedive events are held here with training and safety support.

• Visibility: 4–8 m depending on season and conditions

• Depth Range: up to ~27 m near central lake areas

• Water Temperature: cold year-round; surface waters warm modestly in summer but generally cool (likely under ~20 °C in summer and near freezing under ice in winter)

• Water Conditions: freshwater, cold, seasonal ice cover in winter

• Seasonality: Year-round access with open-water freediving in warmer months and ice freediving events in winter

• Transportation: Road access from Helsinki/Riihimäki area to site located near Melkuttimentie in Loppi, on-site parking

• Local rules: Follow safety guidance from local freediving organisers; respect natural area protections