Mexico has a great diversity of aquatic ecosystems. The Pom-Atasta fluvial system lagoon is part of the Flora and Fauna Natural Protected Area: Laguna de Terminos. It is a region with large areas for manatee (Trichechus mananatus manatus) distribution. This species was included in the list of Mexican species at risk, (NOM-059-and IUCN). In 2013, monitoring was conducted during three seasons; rainy, dry, and north wind. The visual recording of merely 3 animals was blamed on the increasing use of the coastal shore by human activity; usage that has fragmented many areas that were formerly occupied by manatees. Their habitat is now shared with development areas and anthropogenic activity.There are large amounts of organic matter found in this lagoon system; a result of the numerous tributaries of the rivers. The minimum salinity (0.32‰), indicates that lagoons have a strong freshwater influence. Some sites are observed with salinity of not more than 12‰. Oxygen concentrations ranging from 4.2 to 11.3 ± 1 mg/l. The average turbidity was 60 ± 10 cm; pH 8.5 ± 0.5-9.76 ± 1; the average temperature was 28 to 30 ± 3°C; the average depth was 2.5 ± 3 m. The vegetation condition plant species such as Pontederia cordata, Pontederia rotundifolia, and Eichhornia crassipes were found with traces of manatee browsing. Many studies have recorded those plant species as manatee food. They can also be seen as an indicator of water quality. There has been an adverse change in the available habitat caused by the influence of human communities. This influence is expected to negatively affect the habitat and the many species that occupy it, especially the manatees. They are in great danger of disappearing in this area.

Terminos Lagoon was made a protected ecosystem by the Mexican government in 1994, but it is also the most important center for oil extraction and transportation companies in the Gulf of Mexico, besides several rivers carrying on city effluents along with agricultural and cattle residuals into the lagoon. The main goal of this study is to analyze the potential for aquatic mammal species such as bottlenose dolphins, manatees and river otters to be environmental sentinels. While data showed that levels of heavy metals and pesticides contained in bottlenose dolphins blubber samples -lead (< 1.1 mg/l) and cadmium (< 0.08 mg/l) -were low, heptachlor epoxies showed the highest values (359.67 μg/g), followed by endosulfan sulfate and methoxychlor,' p-DDE, which was recorded in a sample with concentrations of 239.542 µg/g, along with p 'p-DDD and p' p-DDT, with values of 1.2 and 13.63 μg/g, respectively. Analysis of heavy metals in Manatee bones showed that zinc, lead and cadmium presented higher concentrations (102.60 + 27.19 µg/g, 14.54 + 1.77, µg/g and 3.92 + 0.5 µg/g, respectively). Values of both heavy metals and pesticides in samples were low compared to those recorded in other studies. Water quality analysis at the fluvial-lagoon system POM-Atasta found concentrations of BOD 5 of up to 270 mg/l, COD 640 mg/l and SST 245 mg/l. These environmental and biological parameters, combined with the health assessment results for bottlenose dolphins, indicate that dolphins have a good health condition but human activities such as agriculture, livestock, fishing and boat traffic seem to have a chronic impact on the ecosystem and, subsequently, on the aquatic mammals found in Terminos Lagoon.

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Anthropogenic activities generate pollutants that are often discharged, untreated, into bodies of water. The drainage system, known as the Caleta in Ciudad del Carmen, Mexico, is surrounded by an urban area and receives immense amounts of industrial and sewage discharge. Physicochemical analyses were conducted for the water and sediment samples taken along this drainage system to understand its hydrological dynamic and pollutant load. The drainage channel communicates with Terminos Lagoon, a Natural Protected Area, and the Gulf of Mexico. Water and sediment samples were taken at fifteen stations along the drainage channel during the three local seasons: northwinds (January); dry (May); and rainy (October). Physicochemical parameters (pH, temperature, salinity, dissolved oxygen, and total dissolved solids), as well as biological oxygen demand (BOD5), chemical oxygen demand (COD) and total suspended solids (TSS) were measured in the water samples. Heavy metals concentrations (Fe, Cr, Cu, Zn, Cd and Pb) were quantified in the sediment samples. No differences were observed in the physicochemical parameters between sample stations, although differences (P < 0.05) were observed between seasons. Dissolved oxygen levels at all stations and in all seasons were near or below hypoxia levels (< 2.0 mg/l). Biological oxygen demand and COD were highest during the rainy season, particularly near industrial effluent discharges. Heavy metals concentrations varied spatially, with higher levels nearest the drainage outlet and lower levels further inland. Lead and iron levels were extremely high, and all heavy metals concentrations far exceeded legal limits. The Caleta is clearly heavily impacted by discharge from the surrounding urban area containing pollutants generated by anthropogenic