Gross Reservoir

Gross Reservoir Expansion Project will impact recreation

Named for Denver Water’s former chief engineer, Dwight D. Gross, the reservoir was completed in 1954. It serves as a combination storage and regulating facility for water that flows under the Continental Divide through the Moffat Tunnel.

Construction for the Gross Reservoir Expansion Project started April 2022. Due to construction activities and for the safety of residents and visitors, there is no public access to Gross Reservoir recreation areas and amenities on the south side of the reservoir. The following areas are open during construction:

North Shore picnic area and parking lot.
- Parking:
  - Expect the lot to reach capacity early in the day on busy weekends and remain full most of the day. Visitors will be turned away when the parking lot reaches capacity.
  - There is no street parking for safety reasons. Visitors who park illegally in the parking lot or along the road are subject to parking tickets and/or having their vehicle towed.
  - We encourage carpooling to maximize parking spots, as well as visiting on weekdays to avoid crowds.
- Boating and paddleboarding (the Friday of Memorial Day weekend through Sept. 30):
  - Visitors should expect lower water levels during construction.
  - Some areas of the reservoir will not be accessible to ensure safety. On-water recreationists may be asked to leave the water during blasting operations. Do not cross buoy lines and pay attention to all on-site staff instructions.
  - During boating season, Denver Water will have a shuttle available to take boaters from the North Shore parking lot to the shoreline. The shuttle service is subject to weather and staffing.
  - Visitors can hike down a steep single-track trail. The walk from the parking lot to the boat launch is roughly 1/3 of a mile in length.
South Boulder Creek Outlet Trail below the dam.
- Due to heavy road traffic, there will be periodic access restrictions in this area. We encourage visitors to check the project My Map (below) before heading up to this area for closure information.
Winiger Ridge Campground.
- Vehicular access to the campground is typically open from mid-May through mid-November. Some temporary closures are expected, starting in 2025, to ensure public safety during tree-removal activities.
Forsythe Canyon Trailhead hiking.
- There will be some temporary closures, starting in 2025, to ensure public safety during tree-removal activities.
Ice fishing:
- Ice fishing is permitted during the 2023-24 season. Please remember ice fishing is at your own risk. Please follow all signage and staff instructions.

Please note, all areas may be subject to intermittent closures during the Gross Reservoir Expansion Project to maintain public safety. Observe all posted speed limits, signage and all on-site personnel instructions. Visitors are encouraged to check the project My Map (below) before heading up to the reservoir.

Gross Reservoir Expansion Project My Map

By the numbers

41,811

capacity in acre-feet

7,282

elevation at spillway in feet

440

surface acres on the reservoir

10.9

miles of shoreline

% full

Directions

From the Denver metro area:

Take Highway 93 north from Golden to Highway 72.
Turn left (west) on Highway 72 toward Pinecliffe and travel about 7.5 miles to County Road 77/Gross Dam Road. Turn right onto Gross Dam Road.
Follow Gross Dam Road north to the stop sign. Turn right at the stop sign and continue on Gross Dam Road until you reach the North Shore Picnic Area parking lot.
Note: due to heavy truck traffic and planned road construction on portions of Gross Dam Road, there will be periodic, temporary lane closures and flaggers in place.

From Boulder:

Take Flagstaff Road west until it turns into Gross Dam Road and turn left into the parking area. Please be respectful of our neighbors and do not park in the neighborhood past the parking lot.

Activities, rules and regulations

Gross Reservoir: General Rules and Regulations

These rules and regulations are in addition to and do not supersede any otherwise applicable county, state and federal laws. For more information call 303-634-3641.
Public use permitted only from sunrise to sunset.
Body contact with water is not permitted: swimming, wading and cliff jumping are prohibited.
Parking is permitted only in designated parking lots or defined spaces. Vehicles may not be left parked and unattended at any time from sunset to sunrise, even in designated areas. Vehicles parked in “No Parking” zones may be subject to ticketing and/or towing.
Pedestrian use only on all Gross Reservoir trails.
Domestic animals shall be kept on leash at all times. Pet waste must be removed immediately. Pets are not allowed in the water.
Prohibited:
- Firearms, fireworks or any projectile weapons of any kind.
- Trespassing on dam structure or within any fenced area, facility or areas posted with closure or danger signs.
- Glass bottles or containers, except within an enclosed vehicle.
- Depositing litter or waste in any place other than waste receptacles.
- Dumping of household waste or hazardous materials on Denver Water property or in Denver Water waste receptacles.
- Parking trailers, campers, RVs and buses.
- Operating motor vehicles—including cars, trucks, motorcycles, minibikes, snowmobiles, four-wheel drive or other recreational vehicles—outside of areas specifically designated and posted to permit the operation of such vehicles.
- Launching and landing drones or remote-control airplanes on Denver Water property.
- Unmanned Aircraft Systems: UAS or drones are not allowed to launch or land on Denver Water property.

Gross Reservoir: Boating and Paddleboarding

All Colorado Parks and Wildlife boating regulations and statutes are strictly enforced at Gross Reservoir.
Watercraft are allowed between the Friday of Memorial Day weekend through Sept. 30.
Using watercraft during posted emergency closures is prohibited.
During blasting operations, portions of Gross Reservoir will be closed to the public. Recreationists must follow all on-site personnel instructions.
It is Colorado state law that each person aboard any watercraft must possess a U.S. Coast Guard-approved life jacket or personal flotation device while on the water. Children under 13 years of age MUST wear their life jacket/PFD at all times.
All watercraft are subject to U.S. Coast Guard and CPW safety standards and will be subject to safety inspections.
It is unlawful to operate watercraft under the influence of alcohol or drugs.
Only nonmotorized car-top boats are permitted on the reservoir (car-top boats are those that can be lifted onto and taken from the top of a passenger vehicle and are no more than 18 feet in length).
Prohibited:
- Trailer-hitched boats.
- Motorized boats (gas or electric).
- Trolling motors.
- Remote-controlled boats.
- Sailboats.
- Belly boats.
- Single-chambered flotation devices, such as inner tubes and inflatable mattresses (single chambered paddleboards are permitted).
Information on Colorado Parks and Wildlife's aquatic invasive species.
Information on Colorado Parks and Wildlife's aquatic invasive species boat inspections and decontamination.

Gross Reservoir: Fishing

Due to ongoing construction activities at Gross Reservoir, ice fishing is not permitted during the 2022-23 season.
Fishing is subject to all state regulations enforced by Colorado Parks and Wildlife (CPW) statutes. The reservoir will be open to monitoring and enforcement by CPW. Possession limits may apply. For more information, see Colorado Fishing guide.
There is no public access to fishing on the south side of the reservoir.
Snagging kokanee permitted Oct. 1 to Dec.1 only.
Live aquatic bait is strictly prohibited.
Fishing is prohibited from sunset to sunrise.
Fish are stocked annually by CPW at Gross Reservoir.
During blasting operations, on-site personnel may clear areas of the reservoir to ensure public safety.

Gross Reservoir: Hiking

During construction for the Gross Reservoir Expansion Project, all hiking trails managed by Denver Water begin at the North Shore Picnic Area parking lot.
All hiking trails and gated Denver Water service roads are for pedestrian use only.
Visitors must stay on trails at all times.
Visitors must adhere to all Denver Water restricted areas and local private property lines. Violators will be fined.
Some hiking trails may be closed during blasting activity to ensure public safety.
Bikers and equestrians are permitted on Gross Dam Road only.
Forsythe Canyon Trail is managed by the U.S. Forest Service. This trail provides access to Gross Reservoir on the west side near Winiger Ridge.
County Road 359 is available year-round for pedestrian use and provides access to Gross Reservoir on the west side through the Winiger Ridge campground (managed by the U.S. Forest Service).
Twins Sisters Peak trail is not accessible from Denver Water property. This trail begins along County Road 68J. High-clearance four-wheel drive vehicles are required to access this hiking trail.
Denver Water does not manage any off-highway vehicle (OHV) trails near Gross Reservoir. Please contact the U.S. Forest Service Boulder Ranger District at 303-541-2500 or the Boulder County Sheriff's office at 303-441-1500 for details.

Winiger Ridge Camping

Campers at Winiger Ridge are subject to U.S. Forest Service rules and regulations for the area.
Camping is permitted in numbered, designated campsites only (where metal fire rings are present).
Fires are only permitted in designated metal fire rings at designated campsites.
All fires are subject to Boulder County and state fire bans.
There are no bathrooms or waste receptacles.
Camping is limited to 14 consecutive days and 28 days in a 60-day period.
Visitors in campsites #27-31 may be subject to temporary, periodic closures of approximately one hour during blasting operations.
Campsites are first come first serve and cannot be reserved. There are no required fees.
There is no vehicle access to Winiger Ridge via County Road 359 during winter months.

Directions to Winiger Ridge

From State Highway 93, take State Highway 72 (Coal Creek Canyon Road) west toward Pinecliffe — 15 miles.
Turn right on County Road 97 just past the Timberline Fire station — 1 mile.
Turn right on Magnolia Road (County Road 132) — 2.5 miles.
Turn right on County Road 68 — 2 miles.
Turn right on County Road 359 at the Forsythe Canyon Trailhead parking lot.
Continue down County Road 359 to designated campsites and to the Winiger Ridge parking lot.