From Halopedia, the Halo wiki
Sargasso was a human colony world, named for the Sargasso Sea on Earth, that was invaded by the Covenant in 2546. It was lush, with much vegetation and large deposits of water. The population of Sargasso was seemingly quite affluent, as evidenced by the architecture and landscaping on the planet, possibly suggesting that it was a resort world like Arcadia. The planet also had a military base near the town of Belisk.
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