The gulls of Sulphur Bay make their nests each spring on the rocks around the edge of the lake. They do not build nests in trees like other birds. Sulphur Bay provides a warm area for the gulls to live, but it also causes some problems for them. The bay is important habitat for the birds, which can be observed from a nearby walkway with permission. The warm water is caused by heat from underground magma reaching the earth's surface in some places like Rotorua, causing the water to boil.