Amazon River Dolphin Pictures / They are between 8.25 ft (2.5 m) and 9.75 ft (3 m) long and usually weigh around 200 lbs (90 kg). Amazon River Dolphin Pictures / They are between 8.25 ft (2.5 m) and 9.75 ft (3 m) long and usually weigh around 200 lbs (90 kg).