Sampling was done in six sampling stations for one year (August, 2014-July, 2015) to investigate the impacts of makeshift oil refineries on the macro-invertebrates of the Nun River estuary in the Niger Delta region of Nigeria after over 3 years of chronic pollution of this estuary by the makeshift refinery activities. There was also a massive destruction of the benthic and mangrove associated macrofauna of the Nun River estuary and its tributaries. 18 species of benthic macro-invertebrates

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... ibuted among 15 genera and 9 families were recorded during the study. A total of 2, 942 individual organisms were collected in which 41 belonged to the Class Polycheata, 684 belonged to the Class Decapoda (subphylum crustacea), and 2, 217 belonged to the Class Gastropoda. The class Gastropoda, made up of 1 family and 2 species had the highest percentage composition (75.36%) and are the most dominant species of the area, followed by the class Decapoda (23.25%), and Class Polychaeta (1.39%), respectively. About 12 organisms (which were present during the baseline study) were absent during the current study. The biodiversity of the estuary is low. The alteration of the physico-chemical parameters as well as the direct contact with the spilled crude oils which resulted from the makeshift oil refinery activities is responsible for the massive destruction of the macro zoobenthos in the area. The results also indicated that the benthic macrofauna of stations 1 and 3 (the illegal oil refinery camps) were completely destroyed, except for station 3 that had just one species of Sesarma huzardi. Station 1 had THC, pH, temperature, and salinity of 1881.79 mg/l, 5.54, 28.83oC, and 7.87%o, respectively. Similarly, Station 3 had THC, pH, temperature, and salinity of 1907.89mg/l, 5.47, 28.73oC, and 7.92%o, respectively. The high THC in the illegal oil refinery camps coupled with the acidic pH (5.47 and 5.54) and low DO may have caused the elimination of the macrofauna in these stations. The intertidal benthic macro invertebrates of station 2 were also very few, compared to stations 4, 5, and 6. Station 2 had THC, pH, temperature, and salinity of 1810.43mg/l, 5.47, 28.68oC, and 7.9%o, respectively. In a related study, Ekweozor, et al., (1989) undertook a baseline survey of the intertidal macrofauna of the Bonny Estuary and found that Port Harcourt and Okrika sites located in the central portion of the estuary had very low polychaete and total faunal densities with Okrika having a particularly lower number of species in comparison with the other sites, with Capitella capitata being dominant. These low faunal densities were ascribed to pollution of soil (Spies and Davies, 1979; Dauvin, 1982; McLusky, 1982). Levels of total oil and grease in the sediment at the Okrika site were found to: range from 0.13-0.58g/l00g-1 at the least oiled and most oiled stations respectively, values which Ekweozor, et al., (1989) pointed out, far exceeded background levels found in other areas.