I was surprised to get this message, because the commander who found the site "mercury pond" is an earth mage with no water skills.
So I searched around a bit and found this handy sheet here:
http://www.freewebs.com/dominions2/sites.xls
Sure enough, mercury pond is listed as "water 1", which I think means you need a water1 or higher skilled mage to find that site.
I know this is no fault of that spreadsheet, since "mercury pond" in-game has that breaking-wave icon indicating water. What gives?
Since then, anyhow I have become a bit suspicious and frequently check that spreadsheet. Never seen anything like that happen before, but I *have* had mages with skill-1 in a path find sites listed as level-2 in that spreadsheet. Are those just possible errors in the spreadsheet?