I would not have thought it possible for grass seedheads to dam up a creek. But this was happening along a lower section of the Sevens Creek. If you look closely at the you’ll notice the difference in water levels the dam has created. (About 30 cms ). Large fish were trapped upstream of these dams. As more grass seed heads blew onto the creek , they were swept into the barriers adding to their strength. What a great water filter ! There were several of these barriers in this section of the creek . Eventually they must burst and reform at the next fallen branch.