Riverbed dredging is a less common but traditional method of mining Sri Lankan gemstones, requiring the skill and strength of experienced dredgers. Water flow in a stream is temporarily redirected using a barrier, increasing water pressure over a selected point in the riverbed. Teams use long-handled shovels — sometimes over 40 feet in length — to scrape the bottom of the river until the illam (gem-bearing gravel) is exposed.

The flowing water removes lighter overburden material while coarse sand and gravel settle in ridges. Miners then collect and wash the illam by hand, searching for precious gems such as blue sapphires Sri Lanka is famous for. This method reflects Sri Lanka’s generations-old tradition of discovering gems using skills passed down through families.