On September 16, 2025, two engineers from Hatch walked the north shore of the South Fork Dam while water poured over its crest. The overflow limited how much of the concrete they could see, and their report notes that they never reached the south shore at all. Upstream, at Jump Creek Dam, the same inspection team found a siphon pipe hanging dry above a low reservoir, feeding a pair of small turbines in a shipping container beside the spillway.
Those two structures, about 18 kilometres southwest of downtown, hold the drinking water for most of the Nanaimo area. Jump Lake, the reservoir behind Jump Creek Dam, is the city's savings account. South Fork, lower down the same river, is where the water is drawn off. The City of Nanaimo owns and operates ten dams in all, split between these water supply dams in the watershed and recreational dams in city parks, the best known being the pair in Colliery Dam Park.
Jump Lake and the South Fork: two dams on one river
The City of Nanaimo describes Jump Creek Dam as the higher of its two supply dams, holding about 17 million cubic metres in what engineers call active or live storage: the level is meant to rise in winter and fall through the dry months. Hatch's 2025 inspection report gives a more exact pair of numbers, 13.3 million cubic metres with the spillway gates down and 16.8 million with them raised, and the 2022 Water Supply Strategy uses 16.6 million. The main embankment is earth fill around a till core, 464 metres long and 25 metres high, with a smaller saddle dam beside it that doubles as an emergency spillway.
Its age depends on which document you read. The city's web page and its 2007 supply plan say the dam went up in the early 1970s; Hatch and the 2022 strategy both give 1974. The gates that let the city hold back extra water in summer are a later addition, dated to 1987 by Hatch, while the 2007 plan credits a late-1990s modification with raising storage to 16.6 million cubic metres.
South Fork is older and far more striking.
It is an unreinforced concrete arch in a steep canyon of andesite, a variable-radius design that Hatch says has not been structurally modified since it was built. The city gives 1930 as the construction year, its height as 30 metres and its width as 50 metres. Hatch dates it to 1931, measures it at 30.5 to 30.9 metres high, and gives a total crest of 65.4 metres, 50.6 of which is open overflow spillway. It impounds only about 2 million cubic metres. The city keeps it full on purpose, because a constant level gives constant pressure in the pipes leading to the treatment plant.
The catchment figures also shift between documents, and here the difference has a simple explanation. The 2022 strategy gives 52 square kilometres draining to Jump Creek Dam, 209 to South Fork, and about 673 for the whole Nanaimo River. The 2007 plan's figure of 230 square kilometres and the city's current "over 200" describe roughly the same South Fork area.
Forest land the city does not own
None of the land around those reservoirs belongs to the city, apart from the dam footprints, the reservoirs out to their high-water line, a small buffer, and rights-of-way for the pipelines. The rest is privately held managed forest, mainly owned by Mosaic Forest Management, and the city traces the title back to the E&N Land Grant. The names on that ownership have changed over the years: the 2007 plan calls Weyerhaeuser the principal landowner before Island Timberlands, and elsewhere lists Island Timberlands and TimberWest together.
Logging carries on in the watershed. The companies harvest, plant, build and maintain roads, control access and handle fire prevention, under the Private Managed Forest Land Act and, by the city's count, more than 30 other provincial and federal regulations, several of them tied directly to water quality. Island Timberlands completed a watershed assessment in 2001, which produced a management plan, and the assessment was repeated in 2021. The city and Mosaic meet each year to go over plans for the area. The 2007 plan credits better logging practice with a significant drop in turbidity spikes during heavy runoff. The industry still talks in an older vocabulary, with words such as skookum, meaning strong, that came into English from Chinook Jargon.
The water system itself changed hands too. The Greater Nanaimo Water District was set up by an act of the provincial legislature in 1953 to finance and build supply for the City of Nanaimo and the community of Extension. Ownership and operation passed to the city in 2004.
The roots go further back. The city's own history starts in 1879, when the Vancouver Coal Company laid wooden pipes from a spring on Wesley Street, a reminder of how much of early Nanaimo ran on the coal companies.
From the South Fork intake to the tap
Water leaves South Fork through two parallel steel mains, a 750-millimetre line built in 1954 and a 1,200-millimetre line finished in 1993. They feed the South Fork Water Treatment Plant, which the city officially opened in April 2016.
Before that plant, the 2007 plan says the city met provincial rules with chlorination alone, because the raw water was good and access to the watershed could be controlled. Island Health then changed the city's operating permit to require filtration under what is known as the 4-3-2-1 policy: 99.99 per cent removal of viruses, 99.9 per cent removal of cryptosporidium and giardia, two treatment methods, and no more than one turbidity unit in finished water. The plant screens the water, flocculates it and pushes it through ultrafiltration membranes with openings of 0.1 micrometres. Water rejected by the first set of membranes passes through a second set so less of it is wasted. Chlorine follows at about one part per million. Fluoride has never been added.
The 2025 annual water quality report puts the plant's peak capacity at 116 megalitres a day and the population served at about 111,845, reached through roughly 660 kilometres of mains. Treated water goes to the City of Nanaimo, Snuneymuxw First Nation and the South West Extension Water District. Average consumption in 2025 was 37.36 megalitres a day; the peak came on September 10, at 72.197 megalitres. Even a simple count can wobble: the city's history page lists nine balancing reservoirs around town, and the 2025 report counts eight balancing tanks.
Water released for fish as well as people
Most of the water stored behind the two dams is not drunk. The city says the majority is held for fisheries, released to top up low summer flows in the Nanaimo River and sent down in pulses in early fall for spawning salmon. Those releases follow the Nanaimo River Water Management Plan, a partnership of the city, Harmac Pacific, Snuneymuxw First Nation, Fisheries and Oceans Canada and the province, under which the city provides about 25 per cent of the river's environmental flow needs.
Harmac is a large player on the same river. The 2022 strategy says the pulp mill owns a dam at Fourth Lake with 38 million cubic metres of live storage and a licensed withdrawal of 142.9 million cubic metres a year, far more than the city's own annual use of about 14.3 million. Harmac also owns a well field on the Cassidy aquifer, and the city recently built an emergency pump station there capable of 50 megalitres a day in case the South Fork dam or intake were ever compromised.
Lantzville joins the system
Lantzville's own system draws on a district well field.
The Lantzville/Nanaimo Water Agreement was approved by district council on September 8, 2014, and amended in August 2018. Its opening recitals describe a bulk supply arrangement under the Community Charter, with Lantzville also taking part in the cost of other services delivered through the Regional District of Nanaimo. Nothing in the documents the district has posted proposes merging the two municipalities.
The pipes met at Dover Road, Lantzville Road and Schook Road in 2017, and council set June 18, 2018 as the start of deliveries. A letter to residents that July listed the bill: $676,945.68 for the interconnection and $1,330,258.50 to buy into the Nanaimo system, the latter to be recovered from new connections. The letter said the link could raise the capacity of Lantzville's system by 170 per cent once fully used, with priority going to homes on failing or poor-quality wells. The city's 2022 forecast has Lantzville's draw rising from 207 megalitres a year in 2020 to a most-probable 668 by 2061.
The regional watershed programme
The supply belongs to the city, but the wider question of how land use affects water across the region sits with the Regional District of Nanaimo's Drinking Water and Watershed Protection program. It was established after a 2008 referendum, launched in 2009 and paid for by a parcel tax that started at $12, fell to $8 when the member municipalities joined and now stands at $16. All seven electoral areas take part, along with Nanaimo, Parksville, Lantzville and Qualicum Beach.
The RDN is frank about its limits. The program has no regulatory authority; water licensing, drinking water systems and fisheries remain provincial and federal jobs. Its role, in its own description, is to be an advocate, convener and facilitator, gathering local stream and aquifer data that senior networks miss. A technical advisory committee of 23 members includes a City of Nanaimo representative and a seat for Mosaic Forest Management.
Reading the river from Nanaimo River Road
You cannot walk up to the intake, but you can see the system at work downstream. The city warns that releases from the two dams can make the Nanaimo River rise or fall daily, sometimes with little warning, which changes currents and hides snags. If you swim at the RDN's Nanaimo River Regional Park, a 56-hectare stretch of mature Douglas-fir off Frey Road, those changing levels are part of the river you are swimming in. Other rivers, beaches and parks in the region are collected under Land and Sea.
The other sign is on your lawn. Stage 3 watering restrictions were in effect in Nanaimo when the city last updated that page on October 1, 2026, asking households to keep lawn watering to one day a week. The 2022 strategy, meanwhile, expects that raising Jump Creek Dam will not be needed until beyond 2061.
South Fork is the open item. A 2002 assessment by Sandwell found that ground motion from a 1-in-2,500-year earthquake could compromise the arch and possibly breach it, and the 2022 strategy says the city plans a roller-compacted concrete stabilization berm first recommended in 2001. Hatch's report on the September 2025 inspection rates the dam "Very High" consequence and makes no mention of a berm.
Questions
Where does Nanaimo's drinking water come from?
It comes from the south fork of the Nanaimo River, in a forested catchment southwest of the city. Rain and snowmelt collect behind Jump Creek Dam, flow down the river to South Fork Dam, and enter the city's intake there before treatment.
Is Jump Lake the same as Jump Creek Dam?
They are two names for one place. Jump Lake is the reservoir and Jump Creek Dam is the earth-fill structure that holds it back, and City of Nanaimo documents use both names, sometimes on the same page.
Can you visit Jump Lake or the South Fork Dam?
The city describes access to the supply watershed as strictly limited, and the land around the reservoirs is private managed forest. Its dam safety page also asks visitors to stay well clear of dams, spillways, intakes and log booms and to respect fenced and gated areas.
Who owns the Nanaimo watershed?
Mosaic Forest Management owns most of the land, which the city traces back to the E&N Land Grant. The City of Nanaimo owns only the dam footprints and the reservoirs out to the high-water line, plus a small buffer and pipeline rights-of-way.
Is fluoride added to Nanaimo's water?
No. The city states that fluoride is not added and has never been added to its drinking water. Chlorine is added after filtration at about one part per million.
When did the South Fork Water Treatment Plant open?
The city lists April 2016 as the official opening. Before filtration, the 2007 supply plan says the city met provincial rules with chlorination alone, but an Island Health operating permit later required filtration.
Does Lantzville get its water from Nanaimo?
Partly. Under an agreement approved by Lantzville council in 2014, Nanaimo water began flowing to the district on June 18, 2018. The city's 2022 strategy says it serves Lantzville's upper pressure zone and can supply other parts of Lantzville in an emergency.
Why does the Nanaimo River rise and fall in summer?
Releases from Jump Creek and South Fork dams are used for flood control and fish habitat, so levels can change daily with little warning. In late summer and early fall the city also releases pulses of water to help salmon spawning.
Will Nanaimo need a bigger dam?
Not for decades, according to the city's 2022 Water Supply Strategy. Its modelling suggests raising Jump Creek Dam will not be needed until beyond 2061, and that the treatment plant's 116 megalitres a day should still cover peak demand then.
What is the RDN's Drinking Water and Watershed Protection program?
It is a regional service set up after a 2008 referendum and launched in 2009, funded by a parcel tax across the Regional District of Nanaimo. It gathers water data, supports land-use planning and runs rebates and education, but it has no regulatory power over wells or water licences.
Sources
- Water Supply and Treatment, City of Nanaimo, 2026-07-29
- Watershed Protection, City of Nanaimo, 2026-10-13
- South Fork Water Treatment Plant, City of Nanaimo, 2025-09-26
- Dam Regulations & Safety, City of Nanaimo, 2026-08-11
- Water Quality, City of Nanaimo
- Water Conservation, City of Nanaimo, 2026-10-14
- Watering Restrictions, City of Nanaimo, 2026-10-01
- Annual Water Quality Report 2025, City of Nanaimo, 2026
- 2025 Formal Annual Dam Inspections: Water Supply Dams, Final Report, Hatch Ltd. for the City of Nanaimo, 2026-02-12
- Water Supply Strategy, Final Report, City of Nanaimo, 2022-06
- Water Supply Strategic Plan, City of Nanaimo, 2007-01
- Lantzville/Nanaimo Water Agreement, District of Lantzville, 2021-03-23
- Lantzville/Nanaimo Water Agreement (2014), City of Nanaimo and District of Lantzville, 2014
- Lantzville/Nanaimo Water Agreement Amendment Agreement, City of Nanaimo and District of Lantzville, 2018-08-30
- Letter to Residents: Connection to the Nanaimo Water System, Drinking Water Information, District of Lantzville, 2018-07-16
- Drinking Water and Watershed Protection Program, Regional District of Nanaimo
- Drinking Water and Watershed Protection Action Plan, Regional District of Nanaimo
- Frequently Asked Questions (Drinking Water and Watershed Protection), Regional District of Nanaimo
- Nanaimo River Regional Park, Regional District of Nanaimo
