The Hergelei Natural Reserve is located north of Mangalia, covering a surface of about 98 ha, also known as the Mangalia Lake. This is a thermal and sulphurous marine lake. More than 25 wells are found at the bottom of the lagoon, where one can find bubbles of methane and sulphured hydrogen. The water of the wells has a temperature of about 25 degrees Celsius. Cormorants, ducks and wild geese, swans and pelicans look for shelter in the reeds during winter.