From the website of the organizer:

The small South American country Guyana is located east of Venezuela, west of Suriname and north of Brazil. Dense, tropical rainforest covers more than 80% of the country, which owns more than 15% of fresh water worldwide. Guyana is the only South American country with English as official language. The Jungle of Guyana is home to one of the largest, most exotic and unique wild fish: the prehistoric, massive Arapaima. Torpedo-shaped with large black-green scales and red and orange markings, the Arapaima is streamlined, smooth and incredibly strong.

The Fishing

Also from the organizer's website:

While this trip is definitely not for everyone, it is ideal for those anglers that love to combine adventure travel, technical fishing and the opportunity to catch one of the most exotic and interesting fish on the planet. Arapaima are quite literally freshwater dinosaurs. Found in few places on the planet, the arapaima is the largest, scaled freshwater fish in existence, known for reaching weights of over 700 pounds and lengths of more than ten feet long. The waters that are controlled by Rewa Village are home to impressive numbers of large arapaima, and the fact that the local guides and the Indifly conservation project have worked hard on researching, protecting and understanding these amazing fish has resulted in a very legitimate and successful fly fishing program.

Click here for more information on this trip.