## 5 Conclusions  
Observing and detecting effluent plumes in the marine environment using satellite data is a challenging task because of the particularity of the discharges and the variations in the coastal hydrodynamic conditions. However, this study proved that this approach is feasible for marine outfall plume monitoring, as the Sentinel-2 mission offers enough temporal and spatial resolution, requiring in situ sampling only when necessary. Moreover, a seasonal pattern for the wastewater turbid plume visibility was found within the studied years. The outfall plume was more evident during winter and autumn and was less visible in spring and summer. These findings may be related to the water column's high stratification, lower volume of storm-water runoffs, and sunlight episodes. This preliminary study to support coastal monitoring showed promising results, and hopefully it is just the beginning. According to the ocean color imagery, the coastal drift current and the Aveiro lagoon plume can restrict the superficial dispersion of the submarine outfall turbid plume. However, the sewer plume can reach the adjacent beach and exchange water with the coastal lagoon, mainly in flood tide and northwesterly wind conditions. On the other hand, according to the scant available literature, the sewer plume's concentration was insufficient to harm the water quality of the nearby ecosystems. Thus, it would be an excellent opportunity to implement a new strategy for sea outfall plume dispersion monitoring using ocean color, collecting fewer water samples, and using numerical modeling data to continuously follow the plume's patch. Nevertheless, 20 years out from these studies, the human pressure has increased, and new research was not been carried out. Overall, the next approach for this study would be to investigate the effect of the outfall's turbid plume on the local primary production and to work on automating an algorithm for the outfall's plume detection through Sentinel-2 imagery. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/rs1513368/s1](https://www.mdpi.com/article/10.3390/rs1513368/s1)]([https://www.mdpi.com/article/10.3390/rs1513368/s1](https://www.mdpi.com/article/10.3390/rs1513368/s1)), Figure S1: True color composite from the Sentinel-2 image Level 2 after processing the Level 1 image on ACOLITE; Figure S2: Comparison between the employed algorithm for plume detection. (A) kd490_aasw (B) tspm_nechad2016; (C) t_nechad2016; and (D) t_dogliott; Figure S3: Seasonal average sea outfall catchment area. Conceptualization, B.F., R.M. and J.M.D. ; Methodology, R.M., C.L.L., M.S. and A.P. ; Validation, R.M., C.L.L. and M.S. ; Formal Analysis, J.M.D. ; Investigation, B.F.; Data Curation, B.F., R.M. and M.S. ; Writing--Original Draft Preparation, B.F.; Writing--Review and Editing, B.F., R.M., C.L.L., M.S., A.P. and J.M.D. ; Visualization, B.F., R.M., C.L.L., M.S., A.P. and J.M.D. ; Supervision, R.M. and J.M.D. ; Project Administration, R.M. and J.M.D. All authors have read and agreed to the published version of the manuscript. [PERSON] is funded by national funds through the Portuguese Science Foundation (FCT) under the project CEECIND/00459/2018. Thanks are due to FCT/MCTES for the financial support to CESAM (UIDB/50017/2020+UIDP/50017/2020+LA/P/0094/2020) through national funds. The Sentinel-2 satellite images are publicly available on the Copernicus Open Access Hub [[https://scihub.copernicus.eu/](https://scihub.copernicus.eu/)]([https://scihub.copernicus.eu/](https://scihub.copernicus.eu/)) (accessed on 1 June 2023) and on ONDA [[https://www.onda-dias.eu/cms/services/catalogues/?meta_service_category2=Data-Access](https://www.onda-dias.eu/cms/services/catalogues/?meta_service_category2=Data-Access)]([https://www.onda-dias.eu/cms/services/catalogues/?meta_service_category2=Data-Access](https://www.onda-dias.eu/cms/services/catalogues/?meta_service_category2=Data-Access)) (accessed on 1 June 2023).