The hydrological network had been altered by the development of St. Petersburg through its entire history. When it was founded in 1703, the area was low and swampy and required construction of canals and ponds for drainage. The earth excavated during their construction was used to raise the city. At the end of the 19th century, the delta of Neva consisted of 48 rivers and canals and 101 islands. The most significant distributaries of the delta are listed in the table. Before construction of the Obvodny Canal, the left tributary of that area was the Volkovka; its part at the confluence is now called Monastyrka. The Ladoga Canal starts at the root of Neva and connects it along the southern coast of Lake Ladoga with the Volkhov.