This is not a duplicate of the question asking about the word confluence. This question refers to the point of land created by the confluence.
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The land mass formed by a confluence can also be called a point. A beautiful example is in Pittsburgh, PA. This land mass is formed by the joining of the Allegheny and Monongahela Rivers to create the Ohio River, hence it"s name, "The Pointe", which is the French word for point. The Pointe, Pointe State Park, and the original foundation of Fort Pitt are located on the epicenter of this point.
Although not exactly a single word, however, according to Wikipedia, the phrase river delta can be used to describe the land formation which forms at the point where two rivers meet. From Wikipedia:
A river delta is a landform that forms from deposition of sediment carried by a river as the flow leaves its mouth and enters slower-moving or standing water. This occurs where a river enters an ocean, sea, estuary, lake, reservoir, or (more rarely) another river that cannot transport away the supplied sediment.
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Perhaps its could be termed a peninsula?
A piece of land almost surrounded by water or projecting out into a body of water. — Oxford Dictionaries
Wikipedia mentions peninsula used for the land where a river which courses through a very tight meander which seems similar to OP"s requirement. Assuming here the term can be used regardless for the surrounding waters" direction of flow.
A peninsula (Latin: paeninsula from paene "almost" and insula "island") is a piece of land extending out into a body of water that is still connected to mainland, or a piece of land that is bordered by water on three sides but connected to mainland. <...> The surrounding water is usually understood to be continuous, though not necessarily named as a single body of water. Peninsulas are not always named as such; one can also be a headland, cape, island promontory, bill, point, or spit. <...> A river which courses through a very tight meander is also sometimes said to form a "peninsula" within the (almost closed) loop of water.