in 1699, he was with the group that ascended the mississippi river from biloxi to the "country of the nadouessioux", stopping to overwinter at isle pelée or fort perrot above lake pepin. he went upstream as far as saint anthony falls. after trading with the local dakota bands (the mdewankantons, wahpetons and wahpekutes) in the area, in the summer and fall of 1700 he and a group of 20 men went further up the river known to the native population as "minisota", or "cloud reflected water". this river was known to later voyageurs as the st. pierre, but it is unclear if le sueur knew it by that name at the time. the group continued to the blue earth river, where they built fort l'huillier, named for the chemist who declared it to be copper ore. they overwintered at fort l'huillier, trading furs and other merchandise with the local indian bands. they found the prairies full of bison, and learned to subsist largely on a meat diet. in may 1701, le sueur left a garrison of men at the fort under the command of d'eraque and accompanied a large quantity of the blue earth (dakota language: "makháto") back to fort mobile for further analysis, which revealed that it was not copper and thus worthless. later that year, fort l'huillier was attacked by sac and fox indians. 3 men were killed in the attack on the fort, which was then abandoned.