The East River Ferry joined the new NYC Ferry system on Monday, May 1. View Full Caption DNAinfo/Katie Honan

WILLIAMSBURG — The East River ferry hit a rough patch on its first day as part of the new citywide ferry service after a mechanical issue knocked one boat temporarily out of service.

One of the three boats — which as of 5:30 a.m. Monday morning became a part of the NYC Ferry system — was taken out of the rotation at around 9 a.m. after a loose oil temperature sensor went off, according to a spokesman for the Economic Development Corporation.

"As a precaution the boat was pulled from service and a replacement brought in," spokesman Anthony Hogrebe wrote in an email.

"Because this happened at the tail end of the morning rush, and with ridership getting a boost from opening day, it resulted in some delays for passengers."

The issue left dozens of passengers stranded as delays continued for nearly two hours.

"There are 30 irate people at Greenpoint. We were told to walk to the L. At least get us a bus," Veronica Ades tweeted, asking the mayor to comment.

Service was restored and was operating normally as of 1 p.m., officials said.

The absorption into the citywide ferry service resulted in a cheaper ride, from between $4 and $6 to a flat $2.75 rate.

It relaunched today as the new Rockaway ferry route kicked off for the first time since the ferry put in place after Hurricane Sandy was cut in 2014.

That route, with boats starting at 5:30 a.m., did not have any issues this morning.