"We only have around five hours of archaeology before the tide comes back in," says Wirral Archaeology’s Dominga Devitt.
“Then, when we come back the next day, everything is buried in sand again.”
Despite the ravages of time and tide, the team’s already found much to get excited about.
This spot, between Seacombe and Egremont, could be a rare Viking (or Roman) iron smelting works, known as a bloomery.
Dug into the coastal sandstone, it throws up tantalising questions about our ancient past.
“They wouldn’t have built it to be covered with water twice a day,” Dominga says.
“So the only conclusion is that the Mersey was much shallower back then.”