A machine-accessible medium containing software code that, when read by a computer, causes the computer to perform method for filtering a video in a video system. The method may include generating a foreground mask and a background model from a video, where the foreground mask comprises moving pixels in the video and the background model comprises a statistical description, including a mean and a variance value, for each pixel in the video. Then the background model variance is filtered with a one-dimensional high pass filter in a single orientation. Next, for each linear grouping of pixels in the single orientation of the filtered variance, a first edge pixel is detected between a high-variance group of pixels and a low-variance group of pixels. Then a first waterline position is detected as an area bounded by the first edge pixels.