Map showing drainage basins for the major oceans and seas; grey areas are endorheic basins that do not drain to the ocean.
The "shape" of freshwater
The rivers we see, the lakes we sail on, the swamps we get stuck in - they are where they are because of the physical geography surrounding them.
That physical geography forms what are called Drainage Basins.
A drainage basin is a region of land where water from rain or snow melt drains downhill into a body of water, such as a river, lake, dam, estuary, wetland, sea or ocean.
So a drainage basin includes both the streams and rivers that convey the water as well as the land surfaces from which water drains into those channels.
In essence, the drainage basin acts like a funnel - collecting all the water within the area covered by the basin and channelling it into a waterway.
Each drainage basin is separated topographically from adjacent basins by a ridge, hill or mountain, which is known as a water divide or a watershed.