Subject: Fresh Water Whales

Courtney Stirling Casey (
Thu, 30 Oct 1997 13:15:58 -0500 (EST)

Hey Emily!  Good to hear from you.  You are correct. There are two dolphin
species that live in fresh (or very little salt - called brackish) water
rivers.  They are the Ganges River Dolphin and the Amazon river dolphin,
which is actually pink!

Just like there are fish that live in fresh and salt water, the same
is true with marine mammals.  Physiologically they just have to deal with
salt and water differently.  Living in fresh water requires that all of
the salt that is in the animals tissues does not diffuse (diffusion is
when something like salt leaks from an area of high concentration to an
area of lower concentration, until both areas have equal concentration)
into the surrounding fresh water.  Another way to look at this problem is
to say that animals that live in fresh water need to make sure that all
that fresh water does not leak into them.  Looking at living in salt
water:  animals must make sure that the salt does not leak in and that
their fresh water does not leak out.

These adaptations to living in salt and fresh water are accomplished by
the individual cells that make up the body of the dolphin or fish.  These
cells can move salt and water around in order to keep the animal balanced
(and not wrinkled like we become after sitting in fresh water for long
periods of time).

Does this answer your questions?  Please let me know if you have more
questions or need more help on these.  Say hello to your Mum and Dad for
me (Elizabeth and Nicole also!).  

Love, Courtney

Courtney Stirling Casey
Faculty Research Assistant
Department of Animal and Avian Sciences
University of Maryland

On Wed, 29 Oct 1997, robert murphy wrote:

> Date: Wed, 29 Oct 1997 19:37:07 -0800
> From: robert murphy <>
> To:,
> Subject: Fresh Water Whales
> Dear Cousin Courtney,
> I heard that some whales live in fresh water.  What are the species of
> fresh water whales and how can they live in fresh water?
> Thank You.
> Love, 
> Your cousin, Emily Murphy (age 8)