America’s crop exports are once again at risk due to a diminished Mississippi River.

Months of dry weather and the hottest summer ever shrunk the vital channel that funnels barges of grain and soybeans from the Midwestern crop belt to Gulf Coast ports. Barge operators now are running lighter loads to compensate for the lack of water. Prices paid to farmers for their crops are easing as a result, with seasonal pressure from the autumn harvest further weighing on the market.

Shipping costs for barges along the river surged in September, with spot rates rising as much as 64% in a week at Memphis, Tennessee, according to US Department of Agriculture data. Higher transport costs help make US crops more expensive than shipping out of countries such as Brazil — when bigger South American harvests were already taking market share from North America.

Read More: Shrunken Mississippi River Slows US Food Exports When World Needs Them Most

In Memphis, water levels sank to 10.51 feet below base levels, according to the National Weather Service. That’s the lowest since the historic low-water crest of negative 10.81 feet reached on Oct. 21 last year. Shipping company American Commercial Barge Line predicted water levels could hit last year’s record low by the weekend, prompting more transportation snags.

“Expect delay to transit of 48 to 72 hours due to reduced navigable space in certain areas,” ACBL said in a post on its website.

--With assistance from Dominic Carey.