Jakarta is sinking — and it’s sinking fast, with current estimates predicting half the city will be underwater by 2030.

To cope with the unfolding crisis, the city is building a $10 billion sea wall to keep flood waters out, but that’s only a temporary solution. Parts of the city, home to nearly 10 million people, have sunk over 10 feet in the last few decades, and some areas are submerging at a rate of up to seven inches per year.

The problem is driven by the millions of Indonesians who rely on drawing water up from aquifers that lay beneath the city’s foundation to survive. And since the city was built on-top of marshlands, this practice is directly contributing to the ground’s collapse.

Finding a viable long-term solution has put city-planners, politicians and citizens at odds with one another.

“The only step forward is to evacuate four to five million people, or build this outer sea dike, which gives you another 20 to 50 years to solve all of the problems.” says JanJaap Brinkmann, a Dutch Hydrologist who is working on solutions for Jakarta.

But relocating half the city’s population is easier said than done. Many residents feel passionately about staying in their homes, despite the dangers. And even if they were to leave, planners would still need to address the city’s flawed water infrastructure, which could take years to fix.

As the debate rages on, one thing is certain — the city is sinking fast and something needs to be done immediately.