Beneath the rugged terrain of Nelson Lakes National Park in New Zealand’s South Island, a mesmerizing blue-violet lake stands hidden among steep alpine forests. Fed by the pure waters of Lake Constance, this small body of water is a marvel of nature, boasting “exceptional optical purity” with visibility comparable to pure water, earning it the title of the most aesthetically clear freshwater lake in the world.
Discovered centuries ago by the Ngāti Apa Māori tribe, the lake was revered as Rotomairewhenua, meaning “the lake of peaceful lands.” It served as a sacred site where they performed rituals involving the cleansing of deceased relatives’ bones, believing this practice ensured their spirits a safe passage to their ancestral homeland of Hawaiki.
In recent times, hikers exploring the park have marveled at the lake’s breathtaking color and tranquility. However, it was only around a decade ago that scientific research highlighted the unparalleled clarity of the sub-alpine lake. A visibility range of 70 to 80 meters astonished researchers, who deemed it “the most visually clear freshwater yet reported.”
This extraordinary feature, along with its ethereal beauty, has catapulted Rotomairewhenua to social media fame. Consequently, the lake has become a favored tourist destination from December to March, during New Zealand’s summer season. Alas, with increasing popularity comes rising concern among conservationists and the Ngāti Apa tribe about potential ecological damage to the lake’s pristine waters.
“Lake Snot”: A Threat to Clarity
Their main worry revolves around lindavia, a type of invisible algae nicknamed “lake snow” or “lake snot” for the slimy residue it produces beneath the water’s surface. This alga is already entrenched in downstream lakes Rotoiti, Rotoroa, and Tennyson, posing a significant risk of being transported to Rotomairewhenua via hikers’ footwear or water containers.
Lindavia is present at other lakes in New Zealand, such as Lake Tekapo, where it has caused a nuisance clogging up machinery. – Paul Bryant/Genesis Energy Ltd
Even though lindavia is not hazardous to human health, its mucilage strands can create undesirable concentrations, obstructing fishing gear, boat filters, and hydroelectric systems. Introducing this algae to Rotomairewhenua could compromise the lake’s renowned clarity, posing a threat to both its ecological and cultural integrity.
“We are profoundly concerned,” expresses Jen Skilton, an ecologist and Taiao advisor (environmental manager) at Ngāti Apa ki te Rā Tō Trust. “Should this invasive microorganism reach the lake, it stands to initiate extensive repercussions, influencing water quality and the health of the entire ecosystem.”
Skilton emphasizes the importance of maintaining Rotomairewhenua for future generations. Although the tribe no longer performs ancient rituals there, the lake remains an emblematic part of Ngāti Apa’s identity and spiritual heritage. “We strive to uphold our ancestral traditions and ensure that Rotomairewhenua’s beauty is preserved,” she says.
Visitation Surge and Conservation Efforts
Since 2013, the year of the lake’s clarity research publication, visitor numbers have surged over 100%, according to the New Zealand Department of Conservation. Most tourists reach Rotomairewhenua through two- or seven-day circuits or the Te Araroa long-distance trail, which stretches across New Zealand.
To safeguard the lake’s purity, the Department of Conservation, Ngāti Apa ki te Rā Tō Trust, and Te Araroa Trust have collaborated to implement biosecurity measures along the trail. Cleaning stations equipped with educational materials now line the lakes where lindavia is prevalent, encouraging hikers to thoroughly clean their shoes and gear before progressing towards Rotomairewhenua.
The alpine lake is surrounded by steep forests. – Janet Newell
The conservation community has also emphasized the importance of respecting the lake’s spiritual significance. Signs and videos disseminated on the Te Araroa trail app advise visitors to avoid touching the water, whether for swimming or cooling down. For the Ngāti Apa, entering Rotomairewhenua’s waters is considered a breach of its sacredness, known as “tapu.”
During the busy summer season, wardens from the Department of Conservation or Ngāti Apa representatives often monitor the lake, providing guidance and highlighting the lake’s cultural and ecological value. These wardens also stress the potential risks of not adhering to biosecurity protocols.
Despite the efforts and increased awareness, surveys reveal that the message has not universally resonated among visitors. Many acknowledge reading the cleaning station signs but do not consistently follow the guidelines due to a misplaced belief that they are not the ones causing harm.
Balancing Opportunity and Responsibility
Recognizing the challenge, the Department of Conservation prefers not to restrict visitation due to the lake’s national park status. Instead, they aim to cultivate awareness about the broader environmental impacts of human activity in the backcountry.
Griffin, a former hut warden, underscores the inherent tension between enjoying the natural beauty and minimizing ecological disruption. “With more hikers come necessarily higher maintenance costs,” she mentions. “This includes more frequent toilet cleaning, often requiring helicopter access, which brings additional carbon emissions to the environmental equation.”
Nevertheless, Griffin also appreciates the value of accessibility for visitors. “There’s a profound sense of peacefulness when you reach the lake after a challenging hike,” she recalls. “You can hear birdlife, but the water remains serene, and glimpsing its depths is truly mesmerizing.”
Ultimately, Skilton asserts, the balance between increasing visitation and protecting the lake’s unique features hinges on responsible behavior. “All visitors should recognize the lake’s importance and take steps to minimize their impact,” she says. “By complying with the rules, we can uphold its ecological marvels and protect its sacred status for generations to come.”
With the summer season just around the corner, the call to preserve Rotomairewhenua’s pristine condition could not be more urgent. Each hiker plays a critical role in maintaining the lake’s clarity and cultural heritage.
Do you have thoughts on how to balance nature preservation with tourism? Share your insights below and help spread the word about the importance of protecting Rotomairewhenua’s exceptional clarity and cultural significance.