River Hazards: Sieves
Sieves occur where water is flowing through a narrow or contracted passage such as a crack in rock. Individuals and boats can wedge and get pinned in these restricted passages. Many rivers have well-known sieves that are identified in guide books and on paddling websites.
![Water-worn holes in rock bed](https://ke-courses-production.s3.amazonaws.com/asset_files/production/2916/attachments/original/wr_sieves.jpg?1559564858)