<ol><li>Salinity is already under discussion.
3., 4. Max and average depth seem like good candidates for Body of Water.
5., 6. Bridges and islands are already there.
1., 7. Surface area and volume seem like good candidates, too. The reason I'm discussing them separately is that these data for rivers seems pretty thin on the ground. This doesn't mean that rivers don't have measurable surface areas or volumes, just that we might not get much data. (And volume will have to be carefully documented so that it's not confused with discharge or flow rate for rivers, since these are often described as "volume".)</li>
</ol><p>Re-reading your initial post, I'd say that "capacity" and "volume" are two different, if related, measurements. "Capacity" should probably go on a special reservoir type somewhere, if you want to use it, since only artificial lakes really have such a measure. Certainly rivers and oceans don't (at least, for rivers, not in terms of total volume; maybe in height at certain points, but that's both a different dimension and a completely different issue.)</p>
<p>So, to sum up:</p>
<ol><li>Move the properties "surface area", "volume", and "max depth" from the type Lake to the type Body of Water.</li>
<li>Create a new "average depth" property for body of water.</li>
</ol><p>Does that sound right?</p></div>