## 5 Conclusions  
This study demonstrates the notable role of cyanoprokaryotes in the late summer phytoplankton of 2019 and high diversity of toxic _Microystis_ strains in seven (from the nine studied) shallow Bulgarian waterbodies of high trophic state. All reliably identified strains belonged to two species, namely _M. aeruginosa_ and _M. Wesenberggi_. If _M. aeruginosa_ is worldwide accepted as an MC-producer, the toxic potential of the easily morphologically recognized _M. Wesenberggi_ has long been debated. This work provides more evidence on the existence of toxic strains in _M. Wesenberggi_. The lack of toxicenic _mcyE_ and _mcyB_ sequences from other genera known as potential MC-producers, together with conventional LM observations, allows us to conclude that _M. aeruginosa_ and _M. Wesenberggi_ were the primary MC-producers in the investigated wetlands in August 2019. Moreover, the fact that only MC-LR was detected in water samples from the sites where both species were found (separately or together), suggests that they were associated with the production of this dangerous cyanotoxin. This finding is important as both _Microystis_ species occurred in low amounts in waterbodies dominated by the filamentous heterocytous _Dolichospermum_ or _Aphanizomenon_ s.l. or, more rarely, of the filamentous non-heterocytous _Planktonlrix_. On the background of notable quantitative role of cyanoprokaryotes assessed by pigment marker analysis and conventional LM observations, the proved high genetic diversity of marker _mcy_ genes-bearing strains demonstrates the need for diversification of methods applied for cyanotoxin detection in the studies of vulnerable to CyanoHABS shallow Bulgarian waterbodies. On the other side, the comparison of results from the applied LM and PCR methods once more proved the possibility genetically to detect toxigenic algae, even when they occur in low amounts, but also showed again that currently available genomic sequences are still insufficient to fully resolve the species identification among cyanoprokaryotes and specifically in the genus _Microystis_.  
Conceptualization, M.S.-G. and B.U.; sample collection, B.U., M.S.-G., J.-P.D., G.G. and M.R.; molecular genetic analyses, K.S. and M.R.; investigations by LM, M.S.-G., G.G. and B.U.; HPLC pigment marker analyses, J.-P.D.; HPLC toxin analyses, V.P. and M.M.; resources, B.U. and M.S.-G.; writing, original draft preparation, M.S.-G.; writing--review and editing, M.S.-G., J.-P.D., G.G., B.U., M.R. and K.S.; funding acquisition--B.U., M.S.-G., M.R. and G.G.; project administration, B.U. All authors have read and agreed to the published version of the manuscript. This research was funded by the Scientific Research Fund of the Ministry of Education and Science of Bulgaria (SRF-MESB), grant numbers KP-06-OPR06/2/18.12.2018 and KP-06-OPR03/18/19.12.2018.  
Not applicable.  
Data Availability Statement: Data available in a publicly accessible repository. The data presented in this study are openly available in [NCBI] at [[[https://www.ncbi.nlm.nih.gov/](https://www.ncbi.nlm.nih.gov/)]([https://www.ncbi.nlm.nih.gov/](https://www.ncbi.nlm.nih.gov/))], reference number [MW187787-MN187820 and MW218898-MW218902].  
The authors would like once more to acknowledge SRF-MESB for projects granting and the European Cooperation in Science and Technology, COST Action ES 1105 \"CYANOCOST--Cyanobacterial blooms and toxins in water resources: occurrence, impacts and management\" for adding value to this paper through networking and knowledge sharing with European experts and researchers in the field.  
The authors declare no conflict of interest. The funders had no role in the design of the study, in the collection, analyses, interpretation of data, in the writing of the manuscript, and in the decision to publish the results.