The Environment Ministry has drawn up a list of the nation's 500 most important wetlands to be included in a national biodiversity strategy, it announced Thursday.
The strategy will be revised this fiscal year and will be used as an information source for future preservation efforts.
Hokkaido was home to 61 important wetlands, while Okinawa Prefecture boasted 55 and Kagoshima Prefecture 33. Marshes were the most numerous, with 109 chosen, while 103 seaweed beds and 78 lakes or ponds were also selected.
A panel of 22 experts, including specialists on seagrass, coral, insects and birds, drew up the list using five criteria based on the Ramsar Convention on Wetlands, an international accord to preserve and promote wetlands.
Experts looked at whether wetlands were inhabited by endemic or endangered species, their scale and biodiversity, whether they host a significant percentage of important plant and animal species, and whether they are indispensable to any wildlife.
More than 13 types of wetlands were selected, including coral, grass marshes, rivers and shoals.
Attention was also focused for the first time on seaweed beds, groundwater, springs and man-made waterways, officials said.
Ministry figures indicate that there are 2,196 inland wetlands; the government is also taking stock of coastal wetlands. Officials estimate the national wetland tally will come to around 5,000.