**6. Conclusion and recommendations for further study**

In the analysis that has been conducted which adopted an approach from a seasonal standpoint, it was not evident from the results of the parameters used for monitoring that there was a considerable variation in the results between the different collection points (LRF1 to LRF6). On the other hand, it can be argued that in general (with regard to all the points monitored), the spring of 2018 was the season of the year that had the most significant alterations. When compared with the previous springs (those of 2014, 2015, and 2016), it was also shown to have undergone most alterations in the parameters that were analyzed.

It is worth stressing that the blooming of the algae occurred in December 2018, as the result of the combination of two factors: the availability of nutrients and the suitable conditions with regard to temperature and salinity. High temperatures were found in this period, which favored lower levels of oxygen in the water column, as well as heavy rainfall which led to a large input of nutrients going to the Lagoon.

In addition, there was a period of failure in the floodgate management which affected the entry of water from the sea and hence heightened the problem of the reduction of the values of salinity, which is an important (if limited) parameter for the establishment of *Synechocystis* spp. At the end of the blooming period of these algae, there was a large fish mortality caused by anoxia. In view of this, attention should be paid to the influence of the Rua General Garzon Canal (notorious for its contamination) in the LRF when its floodgates are opened. For this reason, there is a serious need for a suitable management of floodgates that comply with the guidelines of the protocol of the Municipal Contingency Planning of the Rodrigo de Freitas Lagoon. By analogy, the desludging operations of the Jardim de Alah Canal are of extreme importance. As reported earlier, even gentle breezes can mix with the column of water and favor the horizontal uniformity of the water mass, while specific alterations can influence the Lagoon as a whole.

On the basis of the detailed results, it can be argued that particular places in the Lagoon are more prone to the harmful effects of the illegal dumping of sewage, such as those close to the General Garzon Canal and also the Jardim de Alah Canal. However, in light of seasonal factors, it cannot be stated which points undergo a significantly more serious impact from the release of sewage, and further continuous monitoring is needed together with more detailed analyses to make this determination.

At all events, it is of crucial importance to carry out the monitoring and surveillance activities of the illegal dumping of waste material. This should be undertaken in a systematic and continuous way at the customary outlet points with a view to detecting and eradicating these illegal systems. Tests should be carried out to detect the origin of these clandestine practices in the drainage system and include dyes and tracers in the piping, upstream and downstream, beginning with the places where these practices are occurring. This can be assisted by drawing on the records available of the sewage systems (CEDAE) and drainage networks (RIOAGUAS), as well as information about the respective operational districts that are responsible for the maintenance of these systems. Setting out from a clear idea of the origins of the clandestine and illegal practices, a specific study should be undertaken to adjust these situations of non-compliance. This can entail introducing a project about sanitary sewage disposal which can make the economic infrastructure of the area viable without the need to be interconnected with a completely separate waste disposal system.
