Threats to shipping on the Mississippi and the Black Sea are threatening global food supplies.

(Originally published Oct. 14 in “What in the World“) As the war in Ukraine intensifies, Moscow has issued new conditions for renewing the agreement allowing Ukrainian wheat exports from Black Sea ports.

The original agreement expires Nov. 19. Since shipments resumed in July, Ukraine has managed to export about a third of the stockpile created since the invasion in February. But inspectors at both ends are now backed up, leaving almost 100 ships waiting for Turkish inspectors to clear them for unloading. That and fears that Russia won’t renew the export deal have helped send wheat prices to their highest since June.

There’s no word yet on what the new Russian demands are, but they’re likely aimed at alleviating financial sanctions to enable payments for Russian wheat. While the export deal also eases restrictions on shipments of wheat from Russia—the world’s biggest exporter—bars on financial transactions have reportedly prevented Russian wheat from moving. Exports require complex letters of credit and insurance for the shipping companies moving it, and sanctions make banks and insurers reluctant to provide them what they need.

As Moscow threatens to resume its blockade of Ukrainian wheat, the situation for U.S. grain doesn’t look good either. Even as U.S. Army Corps of Engineers work to remove one bottleneck causing grain barges to back up along the Mississippi, drought across the Midwest is leading to low water levels and transportation blockages along the Mississippi’s tributaries, the Ohio River in particular.