There are seven species of River Dolphin. With some more information, We might be able to help with your answer.
not much if it's a baby
big
About 350 pounds.
450 pounds
It depends on the dolphin breed. Sorry I couldn't be very specific.
A baby dolphin weigh about 300 pounds
they weigh about 30 -90 lbs at birth
5 tons
19 tonne.
It depends on what type of dolphin.
They vary in weight greatly - from 10kg, up to 10 tonnes (which is 10000kg). But since I presume you're asking for the common dolphin - a common dolphin can weigh up to 75 kg.
The Boto or Amazon River Dolphin The Franciscana or La Plata River Dolphin The Baiji or Yangtze River Dolphin The Ganges River Dolphin or Susu (Platanista gangetica), The Indus River Dolphin (Platanista minor)