Well I'll be dipped, Lake Ore is a thing.
Yes, the pun was intended.
from
Iron ores and iron works in Finland, 1809–1884
https://www.tandfonline.com/doi/pdf/10.1080/03585522.1953.10409903"The mining of iron ore continued to decline. By the 1870's slightly over I % of
the ore used in the production of pig iron came from Finnish mines. At most of
these all that remained of earlier endeavours were empty and derelict pits. Yet
only a quarter of the industry was dependent on imported raw material. During
the worst days of the iron ore shortage, increasing attention was paid to the
deposits of
lake ores: lumps of ore which had been formed in the bottom mud of the lakes and which, in the opinion of some eager prospectors, were renewed like a felled forest. But these treasures could be found only in the remote districts of
the water-sheds in the neighbourhood of Suomenselka, in the outlying areas of
Savo, in the border regions of Carelia, and in Kainuu. The ancient iron processing
techniques of the peasants had never been completely forgotten and many
primitive bloomeries were erected in Eastern Finland as late as the 1830's and
1840's; after 1835 they enjoyed substantial tax reductions. The bar iron produced
thereby contained some phosphorus, though a lower percentage than that in the
pig iron made in the blast furnaces from the lake ores. Hence it was suitable for
forging. The bar iron found a market in St. Petersburg, and in the period after
the middle of the century a great many bloomeries were enlarged into ironworks
producing wrought iron.
In the early 1850's the amount of lake and bog ores lifted exceeded that of rock ores mined; in the 1870's it totalled some 300,000
skeppund (I skeppund = 400 lbs.). By way of comparison it might be mentioned
that under the pace treaty of Hamina, Sweden guaranteed to Finland a quota of
less than 24,000 skeppund. For the first time the Finnish iron industry enjoyed
prosperity - however short-lived"
While the article is a much later period it does mean "lake ore" isn't a fanciful creation. Ir does refer to lake ore a a historical activity.