Quicksilver Fountain is a rare Artifact card from Mirrodin (MRD), collector number 233. Current market price: $3.65 (foil $13.97), TCGplayer market prices via Scryfall.
At the beginning of each player's upkeep, that player puts a flood counter on target non-Island land they control of their choice. That land is an Island for as long as it has a flood counter on it. At the beginning of each end step, if all lands on the battlefield are Islands, remove all flood counters from them.