The phrase "to stem the flow" means to take action to slow down or stop something from continuing or spreading.
Sentences with «to stem the flow»
He agreed with previous comments from the home secretary that it is essential the government stem the flow and supply of guns if it is to reduce violent crime. (politics.co.uk)
However, if he addresses the «nothing major» leaks reference above, he might just stem the flow from his wallet. (biggerpockets.com)
Other steps to stem the flow of oil are both slow and unproven. (newscientist.com)