Colorado River Mile -12 Slough Channelization

Dates and times are subject to change. This information will be updated as needed.

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Working to prevent the spread of nonnative fish below Glen Canyon Dam

A project in Glen Canyon National Recreation Area will prevent warm water nonnative fish species from spreading in the Colorado River below Glen Canyon Dam. Reshaping the slough at river mile -12 below the dam to enable water to flow more freely will hinder reproduction of nonnative smallmouth bass at this location and deter the fish from spreading further into Glen, Marble, and Grand canyons.

 

Anticipated Hourly Flow for Friday May 9, 2025

Hour System Time (MST)	Total Release (CFS)
0:00	8,700
1:00	8,700
2:00	8,700
3:00	9,800
4:00	10,382
5:00	10,382
6:00	10,382
7:00	10,382
8:00	8,700
9:00	8,700
10:00	8,700
11:00	8,700
12:00	8,000
13:00	5,500
14:00	5,000
15:00	5,000
16:00	9,000
17:00	10,382
18:00	10,382
19:00	10,382
20:00	10,382
21:00	10,382
22:00	9,800
23:00	8,700

 

May 1, 2025 Update

Construction started March 1. Extra measures were taken to reduce sediment in the river. The project is now at the mid-way point. It is still on track for the June completion of the project. BOR is planning reduced water flow for the slough project on Friday May 9, to 5k CFS for approximately 2 hours in the early afternoon.

Be extra cautious—water levels can change fast. Boaters, expect shifting river speeds and newly exposed rocks. At low water, boats can get stuck; at high water, they can drift off if not tied down properly. Campers, if water is rising, set up camp well above the high-water line to avoid flooding. Stay alert and stay safe out there!

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Construction Timeline

Construction is planned to start at the -12 mile slough on March 1, 2025. To prepare for that start date, equipment staging and movement will begin next week (February 24-28). On Wednesday, February 26 a barge will be assembled at Lees Ferry from approximately 7 a.m. to 1 p.m. During this period, access to the river from the dirt boat launch at Lees Ferry will be restricted for public safety as a crane moves barge sections from semi-trailers into the river. The contractor may have 30-minute breaks between barge sections so boaters can access the river. Full access will resume once the barge sections have been put into the river. On the morning of Thursday and Friday, Feb. 27 and 28, construction equipment will be loaded onto the barge from the concrete ramp. Access will be restricted during this period as well, though this process should take less than an hour each morning. Boat traffic may be slowed as the barge transports equipment to the slough and back on Feb. 27 and 28. Further details about delays will be shared in social media posts and website updates.

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Project Images

Images of the slough project in progress.

 

Map of -12 Mile Slough

NPS

Construction progress, 4/30/2025

NPS

Work continues at the slough project, 2/27/2025

US Bureau of Reclamation

Backhoe at the slough project 2/26/2015

NPS

Tug pulling barge to slough project, 2/26/2025

NPS

Barging up the Colorado River to the slough project

NPS

Barge to carry equipment is placed in the river at Lees Ferry, 2/26/2025

NPS

Colorado River Mile -12 Slough in Glen Canyon. The boat s driving upstream, past the lower slough.

NPS