These are geo-thermal subterranean piloted aquarian flows created from the phenomena called "Hot dry rock geothermal energy retention and hydrological evulsion", a condition created by the friction created from the lithospheric and asthenosphere layers compressing and contacting in any given area where shifts in the tectonic plates forming the continents contact and are forced under pressure into rubbing below the mantel and crust of the earths surface. This tends to create "shear strength free-zone heating", and extracts hyrological masses form near by deposits creating a relatively low viscosity flow compared to standardized liquid geological time scales. As the liquid heated produces pressure that results in the asthenospheris venting visible to some as either an escape of pressurized vapor or actual lithospheric liquid (water) which occassionally and randomly can occur under trafficable marine waterways. But all of this is of benefit as the process insures the stability of the mantle's asthenosphere layers.

But correct me if I'm wrong.........

Hey, maybe the river is just "passing gas"?