“Nori doesn’t grow naturally in flat sheets. Instead, it collects in little dark green Vandyke beards on rocks or other objects ranging in depth from the tide-line to 25 feet below the surface on the oceans all around Japan. Collecting it from the sea was difficult and even a little dangerous until the 17th century Tokugawa era, when the Shogun Ieyasu Tokugawa decided he wanted fresh fish served to him on a daily basis. He assigned the fishermen of Shinagawa, a town at the mouth of the Sumida River on the southeast edge of what is now Tokyo, the task of providing the fish.
“The fisher men built weirs to keep a steady supply of fish at hand. Before long, they noticed the wooden struts of the weirs were sporting lush bushes of algae, tasty algae of the sort that had previously been harvested only in the wild. Thus was born the nori aqua-culture, which made the tasty treat more affordable.”
– The Connoisseur’s Guide to Sushi: Everything You Need to Know About Sushi Varieties and Accompaniments, by Dave Lowry, 2010
In the Edo period, Shinagawa was the first post town a traveler would reach after setting out from Nihonbashi on the Tōkaidō highway from Edo to Kyoto.
During that time, Shinagawa also developed a reputation for its tasty nori (laver), once harvested just offshore. Fishing was a second source of income, and Shinagawa regularly supplied seafood to Edo castle. By the 1960s, though, Tokyo Bay had grown too sullied to support aquaculture.
Also, construction of the Tokyo Monorail, as part of the city’s preparation for the Summer Olympics, over water in 1964 along the coastline resulted in the complete elimination of all nori farming in the area.