Mabaruma is only realistically reached by air. Trans Guyana Airways operates scheduled flights from Georgetown's Ogle Airport, and the journey takes under an hour. Book in advance — seats are limited and the flight is the main lifeline for the town's supplies as well as its people.
An alternative is a multi-day boat journey up the Barima River from the coast, but this is slow, uncomfortable, and not regularly scheduled. Most travellers who make this trip are doing so as part of an organised Shell Beach turtle-watching tour that includes all logistics.