DETROIT — At least 300 demonstrators marched through downtown streets on Friday, protesting a move by the city’s Water Department to force tens of thousands of delinquent customers to pay up or face a cutoff in service. From the Cobo Center to Hart Plaza on the banks of the Detroit River, protesters chanted, “Fight, fight; water is a human right.” Others carried placards that read “Thirsty for Justice.”

The Detroit Water and Sewerage Department began cracking down on accounts in March. The number of delinquencies swelled over the winter when the department, fearing frozen pipes, continued to provide service to customers with past due accounts. From March to June 30, the department interrupted service to 15,200 customers, said Greg Eno, a department spokesman. About 92,000 customers are at risk of having service cut off, meaning they are at least 60 days past due or more than $150 behind.

In a statement released on Friday, however, Kevyn D. Orr, the city’s emergency manager, said that of the accounts where water was suspended, more than half were made current within 24 hours, and service was restored. He said that assistance was available for customers with “demonstrated financial need.”

In March, about half the department’s customers, including businesses, had outstanding balances, amounting to $118 million in charges, the department said.