Submerged rock pavement (shown here) would have allowed the indigenous people to control how far their tubers grew, making for easier harvesting.

This harvest came 3,000 years too late.

Hundreds of blackened potatoes were pulled out of the ground at a prehistoric garden in British Columbia, Canada.

Dating back to 3,800 years before the present, the garden was once underwater, in an ecologically rich wetland. And it shows signs of sophisticated engineering techniques used to control the flow of water to more efficiently grow wild wapato tubers, also known as Indian potatoes. [The 25 Most Mysterious Archaeological Finds on Earth]

Archaeologists led by Tanja Hoffmann of the Katzie Development Limited Partnership and Simon Fraser University in British Columbia uncovered the garden during roadwork on Katzie First Nation territory just east of Vancouver, near the Fraser River.

The ancient garden was found during roadwork on Katzie First Nation territory just east of Vancouver, near the Fraser River. (Image credit: Katzie Development Limited Partnership/ Hoffman et al. Sci. Adv. 2016;2:e1601282)

The site had been waterlogged for centuries, resulting in good preservation of plants and other organic materials like wooden tools that would have normally disintegrated over time.

In all, the researchers counted 3,767 whole and fragmented wapato plants (Sagittaria latifolia). Today, these plants are found in wetlands across southern Canada and the United States. Though they were not domesticated, the chestnut-sized roots had long been important to indigenous people, and they are mentioned in some of the first ethnographic accounts of the Pacific Northwest. Explorers Meriwether Lewis and William Clark, for example, were offered wapato roots at a native village near present-day Portland, Oregon. Clark wrote in his diary that the plant resembled a "small Irish potato," and after being roasted, had "an agreeable taste and answers very well in place of bread."

Ancient wapato tubers from the underwater garden site. (Image credit: Katzie Development Limited Partnership)

The ancient tubers that were found in British Columbia had turned dark brown to black in color, and some still had their starchy insides preserved.

The garden had been covered in tightly packed, uniformly sized rocks, leading the researchers to conclude that this was a man-made deposit. Wapato plants can grow far underground, but an artificial rock "pavement" would have controlled how deep the roots could penetrate. This would have allowed the harvesters to more easily find the tubers and pull them out of the muck, Hoffmann and her colleagues wrote in their study, published Dec. 21 in the journal Science Advances.

Besides this waterlogged garden, the archaeological site also had a dry area where people would have lived. The researchers also found about 150 wooden tools that would have been used to dig out the plants.

Radiocarbon dates from the burnt wood found at the site suggest it dates back to 3,800 years ago and was abandoned 3,200 years ago.

The site could represent the first direct evidence of wetland plant cultivation in the prehistoric Pacific Northwest, according to the report on this discovery.

Original article on Live Science.