It is a brackish lake, fresh water and seawater mixing along its length, and elvers used to gather in it in numbers. In 1900 a set of ponds covering about eight hectares was dug on its shore. The man who dug them was Hattori Kurajiro, working with Nakamura Genzaemon, a classmate from the college that is now the university of marine science in Tokyo.

The idea of raising eels rather than catching them took a workable form here. It is a hundred and twenty-five years since the first successful stock was brought on at Maisaka, on the eastern side of the water, and the industry has never left the shoreline it started on.

The water in the ponds today is not lake water. It is pumped up from four hundred metres beneath the Mikatahara plateau, and topped up from natural springs around the lake, and it carries a good deal of dissolved mineral content. The lake gave the industry its reason to exist and then stopped being the thing the fish grow in.

The name of the lake is now the name you see on the menu. What it actually denotes is not something taken out of the lake but something raised beside it. It took more than a century for a place name to turn into a claim about provenance, and almost nobody ordering it thinks about the difference.