back-water

"They've created a couple of dams. In doing so, this is holding back water and it's slowing the flow and it's created this amazing wetland area that's now brimming with wildlife."

This is often called a "water bomb", where the upstream country can temporarily hold back water and then release it suddenly, without warning, causing massive damage downstream.

Trump has lambasted Newsom, saying he has held back water supplies in California and impeded the response to Los Angeles’ recent wildfires.

"They have created five dams and those dams are holding back water. And when we have had a horrifically wet winter like we have just had, we can see the amount of water that is spread out across the land. They are weakening the flow, they're holding more water on the site and they're releasing it slowly into urban Greenford."

Chronic shortages of water from the Colorado River, a key source for Southern California, are also forcing water managers to make plans for scaling back water use.