The government failed to take into account the presence of ecologically valuable marine species at the site of a planned artificial beach in Tai Po before approving the plan, activists will argue in a court challenge to the scheme.
Ho Loy, a member of the Save Lung Mei Alliance, filed a notice with the High Court seeking a judicial review of the government's decision to allow the building of the Lung Mei beach on the grounds of a flawed environmental impact assessment.
The alliance earlier said that preparatory work on the project, first mooted in the 1990s, was due to begin as soon as Tuesday.
The director of Environmental Protection "could not rationally have granted the Environmental Permit on the basis that 'Lung Mei did not appear to serve critical or unique habitats for species of conservation importance, or support significant populations of such species'", Ho wrote in the filing.
The assessment failed to touch on the spotted seahorse, a species classified as "vulnerable" by the International Union for Conservation of Nature, Ho says. It did not consider whether the area around the beach might be a breeding ground for the species.
The applicant also criticised the government's failure to consider three marine species, considered to be of high conservation value, that had been found at the site.
Ho will ask the court to cancel the building permit and order a fresh ecological assessment, which would evaluate measures to protect seahorse breeding grounds near the beach.
The Civil Engineering and Development Department conducted a marine and territorial ecological-impact assessment of all areas within 500 metres of the site in 2006, on the instructions of the Environmental Protection Department. The six-month assessment concluded that Lung Mei "contained mainly low-quality habitats".
The alliance earlier said more than 200 marine species had been recorded by volunteers at the site's rocky tidal habitat - far more than the number in the impact study. And an eight-week survey by the Agriculture, Fisheries and Conservation Department released last month found two spotted seahorses at Lung Mei and concluded that it was "not unreasonable" to expect pregnant or newborn seahorses to be found there.
Before filing the application on Friday, alliance spokesman Peter Li Siu-man said: "We expect the government to cease the project after we file the judicial-review application."
Arthur Lam Kin-kun, spokesman for a group supporting the plan, accused the alliance of abusing the judicial process, and said the majority of people in Tai Po supported the scheme.
The environmental-impact-assessment system has long been criticised. A court challenge in 2010 saw the environmental report into the Hong Kong-Zhuhai-Macau bridge project overturned on the grounds that it failed to meet the government's own standards. The Court of Appeal overturned the ruling.