near the Polish city of two rivers Wagrowiec Velna and Nelba intersect strictly at right angles. A water them, no mixing, then its flow riverbeds further. The secret of this unique phenomenon is the temperature difference between the water in these rivers, different speeds and levels of flows.
Repeatedly experimented here. In Velnu poured red paint, and Nelbu - blue. And at the intersection of the rivers of paint do not mix: red running on track, and blue - on top of the red - in svoe.
See also: In Algeria, there is a lake, where instead of water - ink. Amazon under the second river is not, although the water there. Pink lake on the island of Middle.