Cassini, the gift that keeps on giving has yielded some SAR based topographical maps. This Plan Soc blog has an excellent analysis...

I overlaid the SAR image on top of the calculated topography and I am very, very relieved to report that "lake" stuff is found exclusively in the lowest elevations, the areas that appear in magentas and dark blues on the elevation map, while areas that look like hills have the highest elevations. It may seem like a no-brainer that lakes should be in lows and hills should be highs. But remember that the notion that the materials that look extremely dark to radar are lakes (see also here) has so far been supported only by their morphology -- they're shaped like lakes, and they seem to have channel-like things emptying into them. The topographic map is a new data set, a different kind of data. The hypothesis that the radar-dark things are lakes that are currently filled with liquid can be tested with the topographic data by asking the question: do the lakes fall into topographic lows? The hypothesis has passed this new test with flying colors.

Another similar test is to ask: do the river-channel-like features lie in valleys? And, do their sources lie uphill from their mouths? Again, the answer seems to be yes