This is only cosmetic. Almost all mainland regions have a 20m water height. Some inland regions have other water heights. which is fine. That's how mountain lakes and rivers work. There are four exceptions, regions at the edge of the world with non-standard water heights. This produces a discontinuity in SL's infinite ocean.

These edge regions all have a 7m water height, instead of the usual 20m.

They don't have deep lakes or anything. They're mostly flat land. This is probably some artifact from the early days of SL. It may not be worth fixing but is worth logging.

Attached is a screenshot of what that does, from Firestorm.

I happened to encounter this in Sharpview experimental viewer testing. It raised an internal warning and so I had to chase it down.