A post shared by White Flag Productions (@whiteflagproductions) on Jun 28, 2018 at 1:32pm PDT

People will surf on anything these days. Ocean waves, river waves, wave pools, glacier waves, tidal bores, tanker waves, etc. If it breaks, someone’s on it. It’s hard to find a wave with no one on it. Well, there’s one in Portugal that just might be the strangest novelty wave of them all: Gasoline.

According to White Flag Productions, Gasoline happens when a passenger ferry that runs from Barreiro to Lisbon passes by. If the boat is full, the wave is bigger. That’s not all you’ve got to take into consideration, however.

“There’s a lot of other elements to have in mind if you want to surf this river wave generated by this boat,” White Flag Productions wrote on Instagram, “like tides and winds… We (me and @joaokopke ) had the pleasure to be guided by Ricardo “P1”, the guy who discovered this amazing phenomenon. So, while, Portugal was in a flat spell this day, we scored perfect and long lefts in a river!”