This paper investigates how natural resources can affect firms and supply chains by constraining capacity in critical infrastructure. Combining granular data on firms’ maritime shipping and exogenous variation in the capacity of a major trade route caused by drought, I analyze the effects of disruption on the operations and profitability of U.S. firms. A one-standard deviation increase in water scarcity at a choke point decreases revenues and operating income by approximately 3%. Operating expenses increase with constraints, with the incidence of costs determined by firms' market power. Using data on vessel movement and transportation costs, I show that these effects are likely driven by shipping delays and increases in freight rates. Investors do not appear to fully anticipate the effects, since earnings surprises become more negative even when information was publicly available. Since many economies rely on waterways increasingly constrained by drought, these findings underscore that exacerbating natural capacity constraints can pose significant risks to the economy.