2003 Tuzla Island conflict
A dispute over Tuzla Island in the Kerch Strait arose between Russia and Ukraine in 2003, sparked by unannounced Russian construction of a causeway from their side of the strait toward the island, which is Ukrainian territory. Russians offered various reasons for building the causeway, but Ukraine saw it as a threat to their territorial integrity.
Source: Wikipedia — 2003 Tuzla Island conflict (CC BY-SA 4.0)