What is going on with Gross Reservoir?

Paddle enthusiasts who frequent Gross Reservoir may be surprised by the road closures on the south side of the lake this year.  The closures are due to the commencement in spring 2022 of a massive project to raise the dam and expand the reservoir.  The bad news is that Osprey Point boat launch and all other south side recreational amenities are planned to remain closed through May 2027 (yes, 5 years; no typo).  The good news is that watercraft access to the lake will be maintained from the north shore, near Flagstaff Road, and from the US Forest Service land on Winiger Ridge.  

Reservoir Expansion (GIS Map: Denver Water)

To see an interactive map of current conditions and recreation impacts, scroll down or click here.

This remarkable undertaking will make the hulking concrete mass that is Gross Dam even higher.  At 340 feet, the dam is already one of the tallest in Colorado.  The project will raise the dam crest by 131 feet and nearly triple the reservoir storage (from 40,000 to 117,000 acre-feet).  Some interesting animations and visuals can be found on the project's website.

The capacity expansion will drastically change the landscape and feel of the popular South Boulder Creek arm of the reservoir.  At full pool, the bay next to Osprey point will become much larger.  Most of the existing spur road will be inundated, with the new shoreline lapping almost to the junction with the dam road.  The bay's expanded size will mean greater wind exposure and probably choppier waters.  The meandering South Boulder Creek arm will also be less protected from wind, and will possibly feel more like the central part of the lake does today.  

Additionally, the South Boulder Creek Arm will have a few more meanders as it narrows toward a new inlet location farther west.  The Winiger Ridge of the west side of the lake will have water access of both sides of the peninsula much closer to forest service road 359 than today.  

In the future, you might be able to paddle
above the treetop on this cliff

The most dramatic change to the landscape will be the massive tree removal effort up to the future high water mark.  Fortunately, this isn't scheduled to begin until 2025, so there are a few more seasons to experience most of the lake in its current state. 

Without the ease of Osprey Point, accessing the water at Gross Reservoir will entail some additional effort.  Denver Water has published an interactive map of Gross Reservoir recreation impacts, linked here and embedded below:

The main access point during construction is the North Shore, just off Flagstaff Road.  Vehicle access from the parking lot to the water's edge is restricted by a gate, but Denver Water is running a shuttle for boaters during peak periods (Thursday-Monday, 8 am-6 pm).  Check the green hiker icon on the map above (linked here) for current information in case this arrangement changes.  Outside of the shuttle times, paddlecraft must be toted by hand about 0.3 miles down a service road to the water.  A carry strap, like these from Nozou and iRocker, can be very handy in this situation.    

Winiger Ridge requires a high-clearance vehicle to access via forest service road 359.  The road is open seasonally; check current conditions here.  Like the north shore, water access from this location also involves a moderate carry distance down a fairly steep path.  The walk might be a little further if the water level is down.  Limited camping is available here as well.

If you make it out to Gross during the multi-year construction project, there will still be plenty of water to explore.  It will just take more effort to get to the more familiar southern part of the lake.  You can even imagine yourself paddling in the distant future, at point 100 feet in the air.  Check out our previous post on Gross for more explore ideas and pictures.  Have fun, be safe, wear a PFD, and please respect all construction closures.