Seagrass meadows are important ecosystems for many other species. Nowadays, they are threatened by various factors such as invasive species and anthropogenic impact. For the purpose of preparing this paper, three locations in the area of ​​western Istria in 2020 were monitored, namely: Ribnjak Bay, Funtana Bay and Veštar Bay. A total of four seagrass meadows were found at these locations. The flora in the meadows consisted of the species Cymodocea nodosa and Zostera noltii, and certain algae were found along with the seagrass plants. In the bay of Funtana on the meadow of seagrass Cymodocea nodosa, a large amount of algae Caulerpa cylindracea was observed, which is considered an invasive species in the Adriatic Sea. This algae is considered an invasive species because it is not indigenous to our area and has been found to compete for the space, light and nutrients with our indigenous species and is slowly suppressing them. This is exactly what is happening with the Cymodocea nodosa meadow in Funtana Bay, which has been thinned due to the invasive algae Caulerpa cylindracea. In addition to the invasive species, anthropogenic factors such as coastal construction and embankment, tourism, wastewater, etc. are also a threat.