The rapidly rising tide also flooded the walkway at Marine Lake, with some people needing help from an RNLI volunteer.
Andy Brown, from the West Kirby RNLI launch office, urged people to check tide times before visiting and report any incidents by calling 999.
“Current spring tides are among the highest of the month,” he explained.
“And with the largest volumes of water flowing in at extremely high speeds, the situation can become dangerous very quickly. Large waves can also contain contaminants that can cause serious injury.
“If you are heading to the islands, we advise you to start your journey back to shore three hours before the next high tide and always carry something to keep in touch.”