Generally no worries..but..It would be good idea to leave something like plank of wood what you cat could grip onto if accident should happen...and their claws can rip pond liner in pieces if struggling to get out of water.
My previous dog..being elderly and half blind did mis 'calculate' where to 'park' her bum..and she reversed over the edge and dropped into pond..cold water, old dog that is not very clever with walking anymore, poor eye sight and not even a barker is not good combination..luckily I did notice it in time and got to rescue one very wet, dirty and cold old girl.