I saw some pictures of the water and it looked very muddy and unattractive. Is it always like that?

Colour is always like that with slight changes , specially in winter as temp. drops, due to high quantities of natural sediments arriving from the upper afluents in Corrientes and Paraguay. The bottom of the rivers are muddy.
Usually visitors find the Delta very attractive ,specially Europeans.
I run a independant nautical boat biz in the area , toured New Zelanders, Australians, Canadians , but never Americans ..curious...
The Delta is basically a Jungle ,crossed by many rivers ( almost 300 ). The best time to visit the area is from Sept to end of April.
A spot for nature lovers, fishermen, birdwatchers that also provides good infrastructure for nautical sports.

100 years ago , the wealthiest families used too have their week-end houses , in Tigre city or in a delta Island.

During the last 2 /3 years tourism has slowly but surely grow.

http://welcomeargentina.com.ar/tigre/outings.html

The link above will provide info , pics about Tigre Delta

Yes, water does not look clean but area is still charming. Water is not so dirty that it smells or anything - just muddy. Spent half a day here on recent trip top BA and enjoyed it.

hobbes, How did you go about getting there from BA--day tour?

JaneB, you can take a train from the Retiro station for just a few pesos round trip. Tigre is the last stop on its line, about an hour away; trains leave about every ten minutes, as I recall. When we got to Tigre, we took one of the water taxis and enjoyed lunch at El Gato Blanco, a riverside restaurant.

Thank you GandCT. I'll put this on my list of to-do's for my Jan trip.

There is also a lovely toy train. Take the train from Retiro until La Lucilla then change to the toy train. It is a lovely afternoon activity.

I went to the Delta last year in August. It was nice. I would definately recommend it. Just take a train from retiro like they said and get off at el tigre it's a few blocks or so to the where the boats go. I took a water bus/taxi that had like different stops. It was so different I liked how people actually live on these islands with no cars just boats. I stopped at this place called Tres Bocas and it's little tiny town like a small scale Venice or something. It was nice. I ate at this restaurant away from the main water way I forget the name but it was only 15 or so pesos that's like $5 US and I got fries and steak it was great! I loved Argentina.

The above threads about the Delta rivers refers to what is named first section of the Delta Bonaerense .
Its the more touristy area as it is very close to Tigre city .
Week end houses,hostelrys and " recreos" or bars, are spoted here and there.
I recommend to do this trip anyday but not on week ends.
In summertime gets crowded , the river poluted and noisy.

Historical attractions : the small wooden house that belonged to ex president Sarmiento ( who invented and promoted the Delta)is fully covered in a glass structure to protect it .

There are 4 more sections of the Delta before the Entre Rios Delta ( the most beautifull ).

For the nature oriented traveller, don´t miss ( Unforgettable! ) a visit to the second and third section , crossing the Parana de las Palmas river, with enormous importance regarding History of Argentina and commerce .
After crossing the Parana , navigate the "Capitancito " river to the "Aguajes del Durazno". Stop in the area named "Los Bajos del Temor" for a BBq on board or lunch in Los Pecanes Hostelry.
At noon with the last sun light and bird songs get very romantic....If you enjoy nature , stay for a week end .

Don´t forgett you bathing suit in summer.

I went to Tigre two years ago, taking a river tour and train ride. I thought it was VERY boring. Not much to see.

Ther´s plenty to see and enjoy in the Delta Islands close to Buenos Aires.
Specially if you enjoy rivers , natural sorroundings , birds ,navigation, rowing, fishing in a pure jungle area.

I agree touristy canned tours might be boring or not very attractive.

Santiago, can you tell me how to get to the Second /Third section of Tigre / Is it feasable to go there for a day, and having lunch as you suggest inf Los Pecanes Hostlry?
Do I have to rent a boat or is there a regular water transportation?
In los Pecanes they have a bar b q for lunch?
Thank you.

In Tigre everything is very well organized. When you arrive there, you check the booths there near the water and choose the restaurant you want to go to. You pay at the booth and the next boat will take you there. The boat stops at several restaurants and you get off at your chosen restaurant. We chose a german restautant that is located in a beautiful spot and ate a BBQ steak which was excellent. The couple owning the restaurant is very nice. You then take the the return boat. If you want more information there is a tourist office in front of the booths. We are planing to go back, we enjoyed the boat ride and the restaurant so much.
PELO