Mattenalpsee (or Lake Mattenalp) is a reservoir in the municipality of Innertkirchen, canton of Bern, Switzerland. Its surface area is 18.6 ha (46 acres). The reservoir receives the water from Gauli Glacier. The water is channeled into Räterichsbodensee.

• List of mountain lakes of Switzerland

• Lake Mattenalp^{[permanent dead link‍]}