More than 100 volunteers have been drafted in to help groundskeepers at the Merion Golf Club get the course ready for this week's US Open.
After heavy rain on Friday more rain fell on Monday, meaning practice rounds were suspended until mid-afternoon.
The weather has caused organisers to put plans in place to use two holes on the West Course if necessary.
Asked who might win the tournament England's Ian Poulter joked: "Someone who can use flippers and snorkel best."
Two-time US Open winner Ernie Els added: "You're not going to see a firm US Open this year, I'm sorry.
"I don't care if they get helicopters flying over the fairways, it's not going to dry up."
The course in Ardmore, Pennsylvania has been affected by the remnants of tropical storm Andrea, which is also set to bring an end to the recent good weather in the UK.