All around Stephen Askew was raw sewage, eight feet deep, flooding a crippled waste-treatment plant in Harlem. But Mr. Askew never had a choice; he had to go in.

It was three days after a catastrophic fire damaged the plant and began sending waste into the city’s waterways, forcing the closing of beaches, and workers were engaged in a desperate bid to restart operations.

The temperature inside the plant on July 23 exceeded 120 degrees. Mr. Askew had vaulted over a railing onto a raft floating in the sewage, he said, and paddled to the plant’s backup pump. In the darkness, he stood up in the boat — careful not to overturn it — and opened a nonfunctioning valve manually. The pump restarted and, soon after, the sewage stopped flowing into the Hudson.

“I had to be the captain, I guess,” Mr. Askew, the plant superintendent, said. “If we put any more sewage in the river, it’s going to affect a million people at Coney Island on a 100-degree Saturday.”