Care is needed to determine if a high-water mark is truly accurate.
Find the high-water marks in these pictures
Here are a couple of pictures of Peachtree Creek in Atlanta, Georgia. The pictures were taken on the river bank next to Peachtree Creek a few days after high water occurred during a storm. USGS hydrologists visited the site to try to find out the peak river height during the storm. High-water marks are visible in both pictures, although a hydrologist would only regard one of the marks as being reliable.