Lake Hennessey Has Been Closed to Boats Since 2025. The Trails Above It Just Got Longer.

What is Lake Hennessey for if you can't put a boat on it?

The City of Napa has a clear answer, and it is in the rules. The reservoir in the hills east of Rutherford is a major source of the city's tap water. Recreation on the lake has always come second to that. In January 2025 the city closed the boat launch. As of the Napa County Regional Park & Open Space District's October 7, 2026 status update, the launch is closed "until further notice" and no boats are allowed on the lake. Over the same stretch, the land around the water kept growing. This past summer the district opened a new volunteer-built loop at Moore Creek Park, a short drive up Chiles Pope Valley Road.

The city didn't take away Conn Valley's lake. It made official what the lake already was. The water is off-limits now, and the hills above it are where the recreation is.

Why the Boats Left

The trouble is the golden mussel. The California Department of Fish and Wildlife reported the first known occurrence in North America at the Port of Stockton in October 2024. The mussels are only an inch or two long, but they breed fast, cling to surfaces, and are hard to get rid of. They also travel on boats.

The city's archived notice gave the reason directly. The notice was posted on January 9, 2025, and said the launch was closed because of the golden mussel threat. It gave no reopening date, only "until further notice." Twenty-one months later, the closure is still in place.

The Napa Valley Register's reporting explains why. If mussels reached Lake Hennessey, they could clog the city's intake and delivery pipes. The city's utilities director told the paper that installing ozone equipment at the Hennessey intake to keep them out could cost about a million dollars, plus steep ongoing costs. She did not expect the boating ban to end in the near future. A few boats a weekend can't outweigh that cost. The equipment the lake feeds is already old. The city's current budget lists an active upgrade project for the Hennessey treatment plant, which was originally built in 1983. It plans capital spending of $6 million in 2028, $8 million in 2029, and $20 million in 2030.

Boating at Hennessey was already modest before the closure. The city's published regulations allowed only California-licensed craft with motors of 10 horsepower or less. They prohibited stand-up paddleboards and float tubes, and they banned swimming or any other body contact with the water. The lake was a quiet place to fish from a small boat. Since January 2025 it has had no boats at all.

Shore fishing is less clear. The district's status notice covers boats only and says nothing about fishing from the bank. Before you bring a rod, check the City of Napa's Lake Hennessey Boating & Fishing page for the current rules.

The Same Rule Governs the Shoreline

The city's thinking doesn't stop at the water's edge. The Lake Hennessey Unit of Moore Creek Park is about 900 acres of watershed land. The City of Napa bought it when it built Conn Dam and the lake in the 1940s. The lake is named for Edwin R. Hennessey, a Napa banker who helped get the reservoir built locally after an earlier federal flood control project stalled.

The district's Moore Creek Park page uses the same drinking-water language as the boat closure. Lake Hennessey is the key source of drinking water for the City of Napa, so no contact with the water is allowed at any time. That covers swimming and any dog, horse, or other animal under your supervision. The trails reach the shore, but the rule keeps everyone out of the lake.

That rule also explains how the park is laid out. The main parking area at 2602 Chiles Pope Valley Road splits the park into two units with different rules:

If you're bringing a dog, go south. The district's suggested hikes for the Hennessey side name Chiles Creek Trail, Lake Hennessey Shoreline Trail, Alta Hennessey Trail, Sam the Eagle Trail, and Ken's Cutoff. You can climb the ridges or take the flat walk along the shore.

Where the Recent Investment Went

On the water, the past two years were about keeping things out. On land, people kept building. North of the lot, the district has opened two new trails in recent years.

The first was Moore Creek Trail Redux, built by Redwood Trails Alliance. It runs alongside the fire road on the lower section, then crosses the road and climbs to meet Valentine Vista Trail.

The second opened this summer. The district's June 2026 announcement says the Yip Trip Trail, formerly the Madrone Trail, "has been a long time in the making" and was "100% volunteer-built by hand," with hundreds of volunteers working on it over the years. It is about 3 miles long. It joins Moore Creek Trail near the first creek crossing and again at the top of Washing Machine Trail near the swimming hole. With both ends connected, you can now hike a loop where you used to walk out and back. The district says the route winds through several ecological zones and shows the park and watershed from new angles.

The Yip Trip loop is on the Moore Creek Unit, so dogs aren't allowed on it. That follows from the same layout. The park's northern half has the new trails and the swimming hole. Its southern half has the dog-friendly shoreline and the lake you can look at but not touch.

The practical details are short. Moore Creek Park is open sunrise to sunset. There's no fee, though donations are accepted, and every trail is multi-use for hiking, mountain biking, and horses. The lot fits vehicles of any size and has two equestrian trailer spaces and an ADA portable restroom. There's no drinking water in the park, so bring your own. Moore Creek Park isn't listed among the exceptions in the district's October 7 status update, which means it is open for normal use.

If you'd like to help build the next trail, the district regularly holds volunteer work parties at Moore Creek. They build and repair trails, remove invasive plants, and restore habitat.

If You Still Own a Boat

The nearest alternative is over the ridge on Highway 128, and getting on the water there is harder than it used to be. The threat is also getting closer. Yolo County says the state wildlife department told it on June 25, 2026 that golden mussels had been confirmed in county waterways connected to the Sacramento–San Joaquin Delta.

Lake Berryessa took a different approach from Hennessey. Most of its water goes to Solano County cities and farms, so the Solano County Water Agency leads the prevention effort there, and the lake stayed open to boats with conditions. The agency says Berryessa is mussel-free and is monitored by SCWA, the state, and the Bureau of Reclamation. Under the Bureau of Reclamation's Berryessa boating instructions, a boat can get onto the lake three ways:

1. Quarantine. The boat is inspected and sealed to its trailer with a red seal for 30 days.
2. Decontamination. An approved hot-water decontamination lets you launch sooner.
3. Hand-launched craft. Electric-motor craft still need an inspection. Non-motorized kayaks and paddleboards don't.

Decontamination costs more than when the program started. Reclamation's March 2025 announcement estimated fees of $35 to $150. SCWA's current schedule charges $60 for a simple decontamination, $120 for intermediate, and $170 for complex. Ballast treatment adds $30 for an empty tank or $60 if it hasn't been drained, and there are extra charges for each system beyond five and for every foot of length over 30 feet. Timing also matters this fall. SCWA's decontamination station at Lake Solano County Park closed on Monday, September 7, 2026, and will reopen in spring 2027.

The two reservoirs made different trade-offs for the same reason. Hennessey closed to boats completely and kept its shoreline trails open. Berryessa stayed open and added inspections, seals, and fees. Both decisions come from the same concern: protecting the water first.

Lake Hennessey also shows what we look for when we evaluate land in Conn Valley. Watershed rules, water-contact limits, and who controls neighboring acreage shape how a property can actually be used. The ridge you can see from your terrace may be City watershed land or district parkland, and that affects what you can do there. If you're weighing a parcel near Conn Dam, along Chiles Pope Valley Road, or anywhere the Hennessey watershed reaches, the Jeffrey Earl Warren Team can walk the boundaries with you and help you work out which rules apply.

This article is general information, not legal, tax or financial advice. Consult a qualified professional about your situation.