Bhopal's Bada Talab, also called the Upper Lake is a human-made reservoir. It was built by Raja Bhoj in the 11th century by the construction of an earthen dam across the Kolans River. A twin lake—Chota Talab or the Lower Lake was also constructed nearly 200 years ago, largely from leakage from the Upper. These lakes are surrounded by the city of Bhopal. The Upper Lake is very rich in biodiversity, particularly for macrophytes, phytoplankton, zooplankton, natural and cultured fish species, resident and migratory birds, insects, reptiles and amphibians. A number of bird species are sighted along this lake. Bhoj Wetland, named after Raja Bhoj, is a Ramsar site and a wetland of international importance.