For the past month, as the water level on the lower Mississippi River sinks lower amid an extreme drought stretching from Nebraska to Ohio, a mass of salt water has been pushing upriver from the Gulf of Mexico toward New Orleans, filling the space where fresh water should be. Salt water is heavier than fresh water, so the water forms the shape of a wedge pressing against the bottom of the river. The wedge has already slithered more than 50 miles upstream, passing several small communities in rural Plaquemines Parish, and experts say it will likely reach New Orleans by the end of the month. Even as local and federal officials rush to slow down the wedge, they’re finding themselves powerless against the laws of nature.

The wedge poses a serious threat to the drinking water supply in communities along the river. Salt water has already begun to contaminate local water systems in the towns of Port Sulphur and Pointe à la Hache, and by the end of next week it will likely reach suburban Belle Chasse, home to around 10,000 people. Rural communities in lower Plaquemines Parish have been drinking bottled water and showering in salty tap water for multiple weeks, and it was only this week that officials installed reverse-osmosis filters at the parish’s treatment plant to remove salt from the local water supply.

When humans drink salty water, the elevated sodium in their blood can raise their blood pressure and make their kidneys work harder. This can be harmful for children and pregnant women, as well as those who need to maintain low-sodium diets for medical reasons.

The wedge could cause even more significant health problems as it reaches New Orleans. The city has some 50,000 drinking-water pipes that are made out of lead, and the corrosive salt water would permanently damage those pipes as it moved through the system, allowing lead and other chemicals to leach into water. Research shows that drinking water contaminated with heavy metals can significantly increase one’s risk of brain damage, liver damage, kidney damage, and cancer. Exposure is most dangerous for young children.

Read the full article about climate, clean water and health by Jake Bittle at Grist.