Nature Foundation Report: Fish Die-offs August 7th to 12th 2013

Water Quality Testing Fish Die Off Great Salt Pond August 7th to 12th 2013

Water quality tests were carried out in the Great Salt Pond in order to determine levels of pollution associated with the Fish Die offs which were experienced from the 7th to the 12th of August 2013 in order to determine levels of water quality at that location.


Tests were carried out in order to determine Nitrate, Phosphate, Nitrogen, Dissolved Oxygen, Coliform Bacteria and pH levels. Tests were carried out using both Akton Water Quality Testing Strips and the Lamotte Water Pollution Kit.

1 Methods

Samples were collected at the research sites using standard sampling vials. Once collected the samples were tested for the various levels within 24 hours using the Lamotte Water Pollution testing kit (figure 6) and testing strips. Once levels were measured the data was recorded and stored. pH levels and water temperature were tested in situ using the Oakton Acorn Series pre-calibrated pH meter.

2 Results

Follows are the results gathered from the water quality tests:


2.1 Nitrates (No)

Sewage is the main source of nitrates added by humans to wetland areas. Sewage enters waterways in inadequately treated wastewater from sewage treatment plants, in the effluent (outflow) from illegal sanitary sewer connections, and from poorly functioning septic systems. Water containing high nitrate levels can cause a serious condition called methemoglobinemia, if it is consumed. This condition prevents an infant’s blood from carrying oxygen; hence the nickname "blue baby" syndrome.

Based on research conducted on the 7th to the 12th of August 2013it was determined that the site showed an unusually high level of nitrates considering the norm of less than point two parts per million >.2. The level tested showed a level close to 2.7 ppm

Site #



2 .7 ppm


2.2 Phosphates (Po)

Phosphorus is usually present in natural water as phosphates (orthophosphates, polyphosphates, and organically bound phosphates). Phosphorus is a plant nutrient needed for growth and a fundamental element in the metabolic reactions of plants and animals (hence its use in fertilizers). Sources of phosphorus include human and animal wastes (i.e., sewage), industrial wastes, soil erosion, and fertilizers. Excess phosphorus causes extensive algal growth called "blooms," which are a classic symptom of cultural eutrophication and lead to decreased oxygen levels in wetlands.

Based on research conducted on 7th to the 12th of August 2013it was determined that the site showed an unusually high level of phosphates considering the norm of less than point two parts per million >.2. The level tested showed a level close to .8 ppm

Site #



.8 ppm



2.3 Nitrogen (Nh3)

Ammonia is toxic to fish and aquatic organisms, even in very low concentrations. When levels reach 4 ppm fish can suffer gill damage. When levels reach 5 ppm, sensitive fish can begin to die. As levels near 7 ppm, even ammonia-tolerant fish can begin to die. Ammonia levels greater than approximately 2 ppm usually indicates polluted waters.

The danger ammonia poses for fish depends on the water’s temperature and pH, along with the dissolved oxygen and carbon dioxide levels; the higher the pH and the warmer the temperature, the more toxic the ammonia. Also, ammonia is much more toxic to fish and aquatic life when water contains very little dissolved oxygen and carbon dioxide.

Based on research conducted on the 7th to the 12th of August 2013it was determined that the site showed an unusually high level of nitrogen considering the norm of less than point two parts per million >.2. The level tested showed a level close to 8 ppm

Site #



8 ppm


2.4 Dissolved Oxygen (DO)

Dissolved oxygen analysis measures the amount of gaseous oxygen (O2) dissolved in an aqueous solution. Oxygen gets into water by diffusion from the surrounding air, by aeration (rapid movement), and as a waste product of photosynthesis.

Total dissolved gas concentrations in water should not exceed 15 ppm. Concentrations above this level can be harmful to aquatic life. Fish in waters containing excessive dissolved gases may suffer from "gas bubble disease"; however, this is a very rare occurrence. The bubbles or emboli block the flow of blood through blood vessels causing death. External bubbles (emphysema) can also occur and be seen on fins, on skin and on other tissue. Aquatic invertebrates are also affected by gas bubble disease but at levels higher than those lethal to fish. Inversely gas levels should not go below 5 ppm, which can show a lack of oxygen and can cause fish die-offs and algal blooms.

Based on research conducted on the 7th to the 12th of August 2013it was determined that the site showed an unusually low level of dissolved oxygen considering the norm of approximately seven parts per million (7 ppm). The level tested showed a level close to 1 ppm with a chemical oxygen demand of 700.

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1 ppm




2.5 Alkalinity (pH) and Temperature

A range of pH 6.5 to pH 8.2 is optimal for most organisms. Most organisms have adapted to life in water of a specific pH and may die if it changes even slightly. The toxicity level of ammonia to fish, for example, varies tremendously within a small range of pH values. Acidic water can cause heavy metals such as copper and aluminium to be released into the water. Copper from worn automobile brake pads is often present in runoff. Rapids growing algae remove carbon dioxide from the water during photosynthesis, which can result in a significant increase in pH levels.

Based on research conducted on the 7th to the 12th of August 2013it was determined that the site showed an unusually low level pH considering the norm and temperature. The level tested showed a level close to 6.


Site #





27.5 C

2.6 Coliforms

Increased levels of fecal coliforms may provide a warning of contamination with pathogens due to contact with fecal matter found in sewage run-off which may include contact with the fecal material of humans or other animals. Fecal coliform enters the Environment mainly through human sewage, either from runoff or direct seepage or introduction from sceptic holding tanks.

Some waterborne pathogenic diseases that may coincide with fecal coliform contamination include ear infections, dysentery, typhoid fever, viral and bacterial gastroenteritis, and hepatitis A. The presence of fecal coliform tends to affect humans more than it does aquatic creatures, though not exclusively and can still be harmful to the environment. Aerobic decomposition of this material can reduce dissolved oxygen levels if continuously entered into the environment. This may reduce the oxygen level enough to kill fish and other aquatic life. The unit of measurement which was used during this study was related to a simple Presence/Absence (P/A) scale, with a positive test having a P-vale and a negative test an A-value. The tested location showed a Presence (P-Value) of Coliform in the tested water.

Site #





3. Summary and Conclusion

From the 7th to the 12th of August 2013the St. Maarten Nature Foundation and its has been addressing the fish die off in the Great Salt Pond. The majority of fish in the die off were of the genus Tilapia.


A note on Tilapia:

Oreochromis aureus (commonly known as Blue Tilapia or Israeli Tilapia) is a species of fish in the Cichlidae family. Native to Northern and Western Africa, and the Middle East, through introductions it is now also established elsewhere, including parts of the United States and the Caribbean, where it has been declared an invasive species and has caused significant environmental damage.


The Blue Tilapia is a freshwater fish with a high tolerance for brackish water. Adults are usually 5 to 8 inches (130 to 200 mm) in length and weigh 5 to 6 pounds (2.3 to 2.7 kg); the largest recorded specimen was more than 21 inches (530 mm) long and weighed more than 10 pounds (4.5 kg). Blue Tilapia are mouthbrooders, and broods range from 160 to 1600 eggs per female. O. aureus is primarily herbivorous, but will occasionally consume zooplankton; the young include small invertebrates in their diet.  Oreochromis aureus is native to Northern and Western Africa, and the Middle East, from the Senegal, Niger, Benue and lower Nile rivers in Africa to the Jordan River in the Middle East. Through introductions the fish can be found in the United States in Texas, Alabama, Florida, and Nevada. It has also been established in Central and South America, and Southeast Asia. The original stocks of O. aureus in the United States were from Israel.

Since its introduction into Florida in 1961 the fish has increased its range and frequency of occurrence. It is now the most widespread foreign species in Florida, with established populations as far north as Lake Alice, in Gainesville, Florida. It is a major management problem for the National Park Service due to its predominance in Taylor Slough in Everglades National Park, where it has changed the fish community structure. The species is also expanding its range in Texas, is responsible for inhibition of the population of Largemouth Bass in Lake Trinidad, and is implicated in the unionid mussel declines in two bodies of water in Texas. It is also blamed for a severe decline in native fish populations in Warm Springs Natural Area.

 (commonly known as Blue Tilapia or Israeli Tilapia) is a species of fish in the 

Fish Die-off Incident

Tilapia are an introduced species in St. Maarten, having established themselves over the last ten to fifteen years in the Great Salt and Fresh Ponds. The presence of Tilapia has to be closely studies for the effects on the Native Fish population, however the die-offs of a tolerant species such as Tilapia has to raise concerns about the water quality of St. Maarten.

Since July 2013 the island has been experiencing little rainfall and hot and on occasion calm weather. This, together with land reclamation activities in the Great Salt and Fresh Ponds has resulted in poor water circulation and a drop in dissolved oxygen (DO) levels in the ponds. The Drop in DO has resulted in oxygen depleted water (a DO level close to 1 part per million is essential oxygen depleted compared to a normal level of 7 ppm) which in turn results in fish die offs. The worry is that Tilapia will be the first species to die, followed by Tarpon, Mullets and other native fish species.

The Nature Foundation has relocated approximately 300 tilapia from the Great Salt Pond into the Fresh Pond were oxygen levels are greater, however with the continuous hot weather these fish are also in danger of becoming threatened.

The Nature Foundation would like to echo Governments advice not to eat the fish; doing so might have some significant health consequences.

The Nature Foundation would also like to urge the public to take the necessary precautions and prepare to deal with an unpleasant smell in the Great Bay area. Although the fish are being cleaned there is a risk of a bad smell and also an increase in flies.

The Nature Foundation recommends that the levels of the ponds be continuously managed in order to reflect meteorological conditions in order to avoid further die offs.

The Nature Foundation will monitor the situation closely as they continue.