Two rivers meet in Switzerland. The blue water on the left comes from Lake Léman (Geneva), the turbid water comes from the Arve river, which is full of silt from Mont Blanc and the Chamonix Valley. (Source)
The Gulf of Alaska is informally known as the place where “two oceans meet”, although this is not entirely true. The lighter blue is sediment-laden water from glacial rivers that runs off and meets with the ocean water (dark blue). Since ocean currents are always shifting, the border will fade as the glacial river water mixes with the ocean.
Consider this: A Bucky Barnes/Darcy Lewis story where the two of them meet a la Doctor/River style?
Bucky Barnes, Steven Rogers, Peggy Carter and the Howling Commandos find a strange young woman who knows all of them by their names and very personally in 1945. In particular, she knows a ton about Bucky and seems to have an endless supply of knowledge about the future, but she dies/disappears/something happens before they are able to get to know each other better and Bucky falls in the ice. As Darcy goes bouncing through time thanks to Stark or someone else, she and the Winter Soldier keep meeting in reverse order until in the present day, Bucky, despite his memory loss, knows more about her than she does him.
And then from there, it’s just a matter of turning up that 1940′s soldier charm.
Two of the world’s largest rivers, the Amazon and the Rio Negro, meet but do not mix and are visually distinct but occupy the same body of water. This is due to the rivers’ different speeds and temperatures. -Source