In the crater from Samalas Mountain’s eruption is Lake SegaraAnak taking form of a crescent located around 2009 m amsl with a surface area about 11.126 hectare and depth of 160–230 meter. Due to erosion in the peak and material influx from 1944 eruption the depth of this lake decreases to approximately 200 m only. A research in the year 2007–2008 shows the maximum depth of the lake to be around 205 meter.
With the lake temperature of 5-7o C above ambient temperature, this lake is probably the widest warm water volcanic lake in the world. Water in the lake has Neutral ph (7-8) and water chemistry is dominated by sulfide and chloride with Total Dissolved Solids value reaching 2640 mg/litre showing the flow of hydrothermal fluid to the lake (A. Solikhin, 2010) mixed with rainwater that pour to the caldera.
A fairly flat land in the edge of the lake is used as camping area. There are many activities can be conducted around the lake ranging from camping, hot springs bath, or even fishing because there are varieties of fishes live in the lake. SegaraAnak is also a place for religious ritual called PancakaMulangPekelem which is held by Hindu on every 5 of November.