An apparatus configured to generate a first sonar image from first sonar returns corresponding to a first depth range and generate a second sonar image from the first sonar returns and second sonar returns, the second sonar returns corresponding to a second depth range greater than the first depth range of the first sonar returns such that a portion of the second sonar image does not include sonar return data. The portion without sonar return data corresponds to a period of the first sonar returns and depths greater than the maximum depth of the first depth range. The apparatus is configured to generate and display a fill image for the portion of the second sonar image based on at least one set of side facing sonar return data corresponding to the time period associated with the first sonar returns.