The city may perform "virtual reclamation" to gauge the effects on endangered marine species of creating new land in the western waters.
The idea, floated by the government as an unprecedented move, prompted green activists to cast doubts on its necessity.
The intention was to put barriers in the sea to see how dolphins would react, permanent secretary for development Wai Chi-sing said yesterday. "The test is unprecedented locally and elsewhere in the world," he said.
Samantha Lee Mei-wah, a marine conservation officer from WWF, countered with a question of whether the test might be too dangerous. "This is a world first. How would we know if it would not pose extra stress to the dolphins?" she asked.
Land reclamation is one of the ways under consideration for boosting land supply. But at least three proposed sites - Siu Ho Wan and Sunny Bay, both in northern Lantau, and Lung Kwu Tan in Tuen Mun - may threaten Chinese white dolphins as all three are located near current or proposed marine parks.
Under the idea of virtual reclamation, physical barriers such as shark nets or something similar could be installed along the edge of a site to collect dolphin data and to see if the mammals would seek out an alternative habitat nearby, the Development Bureau said. Officials were working with overseas dolphin experts to decide on the size of the barrier and how it would be built.
The data gathered would complement information collected from a device installed on a hilltop overlooking a reclamation site to monitor dolphin sightings.
Officials hoped the device would fill in the blanks in dolphin data in the shallow coast along the shorelines of the reclamation sites, such as Lung Kwu Tan.
Dr Samuel Hung Ka-yiu, chairman of the Dolphin Conservation Society, called the idea of virtual reclamation "ridiculous".
"You don't need to carry out a test. Just go to the current reclamation site of the boundary crossing for the Hong Kong-Zhuhai-Macau bridge to see if you can still spot any dolphins."
Hung said reclamation work at the crossing, involving more than 100 hectares, had driven the sea mammals away and recent sightings had diminished.
He also questioned whether such a test would require an environmental impact assessment and approval from the director of environmental protection.
Hung, an expert in dolphins, was not invited to a briefing yesterday on the reclamation plans. Only the Conservancy Association, Friends of the Earth, World Green Organisation, WWF and Green Sense were invited.
Green Sense project manager Ho Ka-po said they opposed reclamation that was meant for developing luxury flats. They were also concerned about using Lung Kwu Tan for residential purposes because of its remoteness and proximity to polluting facilities.