From Halopedia, the Halo wiki
The Mimir River was a body of water near the city of Utgard on Harvest. The river started in the Vigrond Highlands, went south of Utgard, and abruptly ended at a waterfall near the Harvest Botanical Gardens. The waterfall turned Mimir's clear water into the murky and slow-moving Slidr River.
A floodlit, well-landscaped trail was found alongside the river, along with numerous scattered bars. The Harvest Parliament Building was found near the river as well. The Mimir River likely evaporated when Harvest was glassed during the First Battle of Harvest in 2525.
Mimir was a primal Norse deity who was renowned for his wisdom.
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