Only female lifeguards will patrol the park during the event, which has triggered a flood of complaints.
Staff will also “guard” the front entrance to “make sure that no males enter the facility”.
In a statement on its Facebook page, a spokesman for WaterWorld said the Sisters Only event would “attract ladies of all religions/beliefs as we invite you to visit our facility and enjoy its features whilst having the option of wearing attire that our normal operating procedures prevent”.
Conservative MP Philip Hollobone said: “I imagine there would be a lot of outrage if the boot was on the other foot and swimmers were told they had to dress appropriately in respect of Christians. I don’t see how this is different.”
One invitation to the “Sisters Only Funday” advises attendees to cover their “awrah” (nudity) by wearing full-length jogging bottoms and a dark-coloured t-shirt.