Heavy rainfall has created a 'poonami' at Harrogate's Royal Pump Rooms according to Harrogate Borough Council, which explained why the museum has remained closed.
The museum was first closed to visitors last Thursday (April 5) after heavy rain hit the town, and has remained closed since.
Explaining the prolonged closure on Twitter today (April 10), Harrogate Borough Council said the outside sewer was 'overflowing with nasties' and dubbed the situation a 'poonami'.
Spokesman for HBC, Andy Carter, said: "Here's why the museum is currently closed. The sewer outside is overflowing and lots of nasties are in danger of flooding us again on the day were were due to open after the last time this happened!"
Mr Carter also said that Yorkshire Water had 'promised to send help, but no-one has turned up'.
Yorkshire Water responded on Twitter asking for the address details of the museum so that the issue could be investigated.