It looks like it was fixed in a previous update, but the bug has now resurfaced. Link to previous reporting of bug https://ludeon.com/forums/index.php?topic=45861.0
Here's some screenshots of I think 18 hives spawning on a river. Note this is with no mods, and is vanilla savage randy commitment mode.
IIRC we decided to allow this since it's kind of cool, there are lots of tunnels with rivers that make this work, and it doesn't really break anything. Thanks for the useful report either way.