Hy Felix,

Probably a microalga or a phycoerythrin rich cyanobacterium... Would you have the opportunity to take a look at what it looks like under a microscope and provide us a picture?

Otherwie you could just pick up a sample and fix it until finding somebody who could help you to determine it... But please let me know what it is if you learn more about it!

Isn't it normal that such swamp waters may be colored red because iron ocher fails? Do you know the iron content / iron concentration or is it possible to investigate?

It should be a sort of red-tide where water is enriched with nutrients.

This water appears too pink to be iron.  To me it looks like runoff from a red clay soil, which I have read to be present in the Antilles.  You would need to examine the water microscopically to determine the source of color.

I agree with Daniel. It looks like runoff from a red clay soil.

I've seen a Mesodinium bloom in mangroves in Belize.

Microscopic pictures needed!

I have seen mangrove leaves floating in coastal water with totally red in color in coastal Narara (opposite to Kalubhar Island) in Gulf of Kutch in Western India,but nothing of the type as shown in the pictures.The waters were murky,but not red.Both Narara & Kalubhar do have plentiful of mangroves.

Red clay run off, micro algae are both possibilities. A microscope would tell the difference...

Agree with other posters that it is too red to be iron

It look like an iron problem.  Are there Rizhopora Mangle or any Rizophora sp?. Are there Avicennia sp. Remember that  Avicenia "help" to the transformations of chemical component of the soil better than RIziphora.. Are there any change of  water salinity?, is there raining season?- I think you need to consider water and in general climate changes.

Mesodinium rubrum forms red-water! Please undertake microscopy and water quality analysis as well.

color looks similar to me to that of cyanophyceae that develop in saltpans waters, see http://www.panoramio.com/photo/57168481

http://www.panoramio.com/photo/57168469

I have often seen comparable phenomena in the lower stretches of the coastal plain of Yemen, bordring (you guess it) the Red Sea. I understood this is caused by the cyanobacterium Trichodesmium erythraeum.  

I have seen something similar in a small pond in the mountains around Innsbruck, caused by Euglena sanguinea

I think that the most probable organism producing this look is the sulfur red bacteria Thiopedia sp. which grow in swamps with high organic matter contents.

Quite a common site in certain times of the year in some mangroves here in the Solomon Islands although not as red as the one you showed in the photos.. Normally referred to as the red tide. Following the period it is not safe to eat shellfish as they may cause paralytic shellfish poisoning. Sometimes may not be as obvious.

Yes during my study on valuation of Andaman and Nicobar Islands Mangroves, I have observed red colour water released from the mangroves area (swamp). But I dont know the reason, But certainly it will be good study to know the facts.

This looks very much like a Cyanobacteria bloom (don't use the wrong terminology "Cyanophyceae"!), but could well be also from other, potentially eukaryotic algal blooms. Without having a sample under the microscope it is difficult, just from these pictures...

I agree that the intense pinkish-red color resembles a Cyanobacterial bloom.  I have seen similar color in salt pans that are flushed irregularly by tides in salt marshes in southern New Jersey.  These are extreme environments.  Isolation from regular tidal flooding  renders these pans  hypersaline for much of the time and also results in wide diurnal fluctuations in temperature (20-35C) and dissolved oxygen (zero to double supersaturation). They can also experience large, sudden salinity drops (40 to 30 ppt) when they are flooded by high tides and when it rains.   I suspect that these extreme conditions (which exclude most other flora and most fauna) may encourage such blooms.  Microscopic examination is necessary to be certain of the organism.

Possibly similar situation here.

http://en.wikipedia.org/wiki/Lake_Hillier#Characteristics

http://funmozar.com/lake-hillier-australia/

Thank you everybody for your comments and advices ! According to local people living next to this small mangrove area, the phenomenon is permanent (my observation was at the end of a long dry season). Fauna does not seem to be disturbed by this pink water as I saw crabs going into. This mangrove consist in a small gully surrounded by Laguncularia racemosa, Avicennia germinans and Rhizophora mangle and isolated from the sea by a sandy barrier. A sewage plant is quite close to the area but not directly upstream. And a similar phenomenon has been observed in another town. I plan to send some samples to a lab for analysis. I will keep you posted about the results.

I have observed a big patch of dark red water about 200 m inland of the coast. Actually this patch of water was due to incessant rains during that time and remained as a stagnant pool of water for quite some time. Later the whole water body turned dark red. I collected a small sample and when I examined it under the microscope found the sample to be full of Euglena sp. I was quite surprised to see what was left after the whole water body was dried up. The entire soil was red in colour, exactly how you have shown in the photos.

Its a red tide phenomenon....microphotogrpahs is required to identify the organism

Dear all,

A local researcher looked at my sample and told me it was Purple Sulfur Bacteria (PSB) but certainly not algae. According to him, this bacteria bloom is interesting and we will look for fundings to look for further phylogeny and ultrastructure studies. I will let you know about the results if we manage to get 2-3K for analysis...

I am working on mangroves ecosystems since 1985, but I didn't seen this phenomenon in mangrove  ecossystem, But I have seen pink , light red and yellow colour blooms in the Inland waters  ( lakes and ponds) of the Andhra Pradesh,India. During the monsoons  surface  waters of the lakes are normally green in colour but later means winter and approaching  to the summer the water colour turns into above said colours. I have collected the water samples for examination, in some ponds colour due to presence of Euglena species (as said by Dr Valsaraj) in some lakes due to presence of Chlamydomonas. This colouring  is due to accumulation of  pigments, when conditions are  not favorable and it is one type of stress physiology. Coming to the ride tide  i think it may  not exist in the estuarine regions.Thank you all.