Lake Spindžius is one of Lithuania's rare "green lakes" — thanks to charophyte algae covering its bed, the water takes on a striking emerald tint in sunlight, though at times it turns completely clear. The lake lies in the Trakai district of southeastern Lithuania, about 9 km east of Aukštadvaris, and is the largest lake of the Spindžius Landscape Reserve within Aukštadvaris Regional Park.

Covering 106.7 hectares, the lake stretches some 2.6 km with a maximum depth of 24.5 metres. It is of glacial channel origin, with a winding shoreline of nearly 7 km, steep wooded banks fed by natural springs — including a strong iron-rich one — and a small island. The Strėva River flows through Spindžius on its way across the regional park, linking it into a chain of some twenty lakes. The lake is almost entirely surrounded by the Spindžius Forest; the Lausgeniai burial mounds lie on its southwestern shore, and a marked nature trail (the Green Trail) runs along the water, crossing the channel where Spindžius meets the smaller Lake Spindžiukas.