One of New York’s busiest bicycle routes has been interrupted this summer by two detours where the city is asking riders to dismount and walk for blocks.

Both work zones cropped up last week without any signage explaining why they were installed or how long they would last. A tipster who asked to remain anonymous reported the detours to Streetsblog, and here are the explanations we got from city agencies.

The first detour is from DOT, which says it is painting the Joe DiMaggio Highway viaduct between 59th and 63rd streets. Crews will intermittently close the bikeway between 8 a.m. and 2 p.m. on weekdays, and cyclists will be directed to the pedestrian path along the river, where they must dismount and walk. DOT said it expects to finish work by the end of August. Observing the detour will add several minutes to bike trips on this stretch of the greenway.

The dismount zone is right next to one of the worst pinch points on the greenway, a section that’s been narrowed to accommodate construction work by the Department of Sanitation at 59th Street. Greenway cyclists will be able to bypass the Sanitation project once a newly-built segment by the water opens to the public.

The second detour is from the Parks Department, which is repairing Dock A at the 79th Street Boat Basin after damage from Hurricane Sandy. The Esplanade is closed entirely, with greenway users directed to the traffic circle by the Boat Basin Café.

That detour first popped up last week, but work has now been postponed until June, said Parks Department spokesperson Sabirah Abdus-Sabur. Construction should last for a few months, depending on weather.