Now, studying Cassini's recent observations of Titan, astronomers have discovered that the lakes in the northern hemisphere are very deep and filled with liquid methane. It was previously known that the deep sea of Titan is deep, but the only lake previously explored is Lake Ontario in the southern hemisphere. It was shallow and the dominant fluid in it was ethane.
And here the lakes of the northern hemisphere are more like the seas, despite the much smaller area and the height above the average satellite surface. The ends of some lakes are hundreds of meters above sea level and some are more than a hundred meters deep.
It has also been established that the surface level of the lakes is changing rapidly, which may mean that lakes are short-lived derivatives. It is possible that they form during the rains and later penetrate the cracks in the surface rocks.
These findings suggest that surface fluids are a significant part of the fluid flow in Titan.