Freshwater cyanobacterial harmful blooms are often dominated by the genus Microcystis, which is a known producer of the cyanotoxin microcystin (MC). In natural populations there is variation in toxin production: not all strains in a population are capable of synthesizing MCs, and MC-producing and non-producing strains co-exist. MC synthesis is encoded by the mcy gene cluster, consisting of ten genes (mcyA-J), and it is generally assumed that the mcy gene cluster is present in microcystin-producing strains and absent among non-producers. In the project applied for, I have performed high throughput sequencing and subsequent bioinformatic analyses. The preliminary results were used in my thesis work, aiming to investigate how mcy genotypes in a Microcystis population influence the ability of a strain to produce microcystins. Preliminary results showed that the studied population contained multiple mcy genotypes, and that microcystin production is not completely linked to the presence or absence of the full mcy gene cluster. However, further work is needed to fully elucidate the link between the mcyA-J genes (the genotypes), and the production of microcystins (the phenotypes). Hence, I apply for a compute project to be able to finish up my last manuscript from my thesis.