The Broads Authority is promoting sustainable boating, and the use of electric boats is being encouraged by the provision of charging points at a number of the mooring sites provided by the Authority. The Broads largely follows the line of the rivers and natural navigations of the area. There are seven navigable rivers, the River Yare and its (direct and indirect) tributaries the Rivers Bure, Thurne, Ant, Waveney, Chet and Wensum. There are no longer any operational locks on any of the rivers (except for Mutford Lock in Oulton Broad that links to the saltwater Lake Lothing in Lowestoft, Suffolk), but all of the waterways are subject to tidal influence. The tidal range decreases with distance from the sea, with highly tidal areas such as Breydon Water contrasted with effectively non-tidal reaches such as the River Ant upstream of Barton Broad. The broads themselves range in size from small pools to the large expanses of Hickling Broad, Barton Broad and Breydon Water. The broads are unevenly distributed, with far more broads in the northern half of Broadland (the Rivers Bure, Thurne and Ant) than in the central and southern portions (the Rivers Yare, Waveney, Chet and Wensum). Individual broads may lie directly on the river, or are more often situated to one side and connected to the river by an artificial channel or dyke. Besides the natural watercourses of the rivers, and the ancient but artificial broads, there is one more recent navigation canal, the lockless Haddiscoe Cut which connects the Rivers Yare and Waveney whilst permitting boats to bypass Breydon Water. There is also a second navigable link to the sea, via the River Waveney and its link to Oulton Broad. Oulton Broad is part of the Broads' tidal system, but is immediately adjacent to Lake Lothing which acts as a harbour for Lowestoft and connects to the North Sea. Oulton Broad and Lake Lothing are connected by Mutford Lock, the only lock on the broads and necessary because of the different tidal ranges and cycles in the two lakes. The River Bure is a tributary of the River Yare which rises near Aylsham in Norfolk and joins the Yare just downstream of Breydon Water. On its way it flows through or passes:   The River Thurne is a tributary of the River Bure.