Pella Strand has been underground for the better part of six weeks. She has filled sixteen survey notebooks, crawled through nine hundred and thirty metres of buried waterway, and discovered a cistern chamber that no living person knew existed. On Tuesday, she found a fish.

It was carved into a keystone at the apex of an arch in the oldest section of the Lower Conduit, approximately forty metres west of the junction where the system splits into its eastern and western branches. A fish within a circle, roughly six inches across, cut with a chisel into limestone that has been wet for a very long time.

“It is a mason’s mark,” Miss Strand said, still wearing the heavy canvas overalls and leather knee-pads she uses for survey work. “A specific one. I’ve seen it in reference drawings at the Polytechnic library — it belongs to the Ashwater Guild of Masons, which operated in Bobington from the 1740s until about 1810.”

The established date for the Lower Conduit is 1782, based on carved numerals found on the brickwork near the Bramblegate Steps outfall. But the mason’s mark sits in a section of the conduit that uses different construction: rougher limestone blocks rather than the uniform brick of the 1782 sections, with a lower, narrower profile and cruder mortar joints.

“The 1782 date is correct for the main system,” Miss Strand said. “But this section is older. The Guild mark, the construction technique, and the stone type all point to the 1760s. Someone built the first section — perhaps sixty or seventy metres — and then the 1782 builders extended it into the full system we’ve been tracing.”

The Seventeenth Notebook

Miss Strand is now working on her seventeenth survey notebook — she goes through approximately one every four days — and the full report is due Friday for submission to the Municipal Works Office and the Heritage Committee.

The report will document the entire system: 947 metres of mapped waterway, the junction and its two branches, the cistern chamber beneath the former Ashwater Brewery, the Bramblegate Steps outfall, and now the older section with its guild mark.

“The fish mark changes the story,” she said. “We assumed this was a single construction project in 1782 — a water supply for the breweries. But the older section runs toward the river, not toward the breweries. It may have been built for a different purpose entirely. Drainage, perhaps. Or an earlier, smaller water supply that the brewery builders co-opted.”

Chief Municipal Engineer Dorothea Kinnear, who commissioned the original underground survey six months ago, said the discovery would be included in the heritage listing submission already before the Municipal Heritage Committee.

“Miss Strand has done rather more than I asked her to,” Mrs Kinnear said, with what might have been a smile. “I asked her to map the drainage. She has found us a river, a cistern, a guild mark, and two hundred and forty years of history.”

The full report is expected to run to approximately sixty pages. Miss Strand said she would finish it by Thursday evening.

“Then I shall sleep,” she said. “I have not been dry for a month.”