Officials at the Eryri National Park hope to promote cultural heritage and want to “standardise” the names to ensure their use in future generations.
This comes one year after the park changed its official name from Snowdonia last year, with Mount Snowdon being changed to Yr Wyddfa.
This latest move means that several beauty spots such as Lake Australia and Bala Lake will no longer be referred to in English, and will take their Welsh names, Llyn Bochlwyd and Llyn Tegid.
Another beauty spot, which is commonly known as Bearded Lake, will now be referenced in future maps and texts as Llyn Barfog.
On Wednesday, the National Park Authority unanimously backed the move in a vote, as Welsh activists continue to campaign for historical sites to be renamed in their native tongue.
Earlier this year, the Brecon Beacons also returned to its original name Brannau Brycheiniog, despite fierce opposition. Both UK government ministers and Welsh Conservatives accused park bosses of attempting to look “trendy” and that the move could “undermine” the region’s international identity.
Welsh Secretary David TC Davies said: “What concerns me is the fact there was no consultation and people who live and work in the national park were not given the opportunity to voice their opinion. It would be somewhat alarming if this was an entirely executive decision.
It has since emerged that Caerphilly and Barry could revert to their native names, as language campaigners push for “Welsh names for Welsh places”.