This is generally the result of a partial blockage. This blockage can be a build-up of hair etc. that has caught on the mechanism of the waste. To check this, simply remove the mechanism (see video), clear away any hair, rinse the mechanism and drop it back into your waste. If this does not rectify the problem, there may be a partial blockage downstream. If so, remove the mechanism and if water doesn’t run away quickly it is most like you have a downstream blockage. Best to call a plumber to deal with this.