Two readings
Kōloa can be read as kō loa, long sugarcane — and the town is where the first commercially successful sugar plantation in Hawaiʻi was established in 1835. But the name is older than that plantation, so the reading is probably retrospective.
Koloa is also the native Hawaiian duck, koloa maoli, still found on Kauaʻi and endangered elsewhere. That reading has the better claim on the original.
The plantation
The 1835 mill at Kōloa set the pattern for the next century and a half: imported labour, consolidated land, and an economy organised around one crop. The last Hawaiʻi sugar plantation closed in 2016.