Abstract <p>Three strains of algal viruses (TvV-SM2, IgV-SS1, and EhV-SS2) were isolated from the coastal waters of the Black Sea in 2022–2023. The first strain causes the lysis of cells of the green algae <i>Tetraselmis viridis</i> and <i>Tetraselmis striata</i>, the second affects cells of the prymnesiophyte <i>Isochrysis galbana</i>, and the third affects the coccolithophore <i>Emiliania huxleyi</i>. No other hosts of the pathogens are detected during the study of possible contact of the isolated viruses with indicator cultures of 32 species of marine microalgae. Viral particles of all three strains have the shape of a regular convex icosahedron, and their diameter ranges from 48 to 174 nm. They are found to have a second membrane: a supercapsid. The titer of TvV-SM2 is 1.3 × 10⁸ virions/mL, IgV-SS1 and EhV-SS2 3.1 × 10⁴ and 2.5 × 10⁵ virions/mL, respectively. The effect of different concentrations of copper ions on the activity of algal viruses is studied for the first time using TvV-SM2 as an example. Under the influence of the toxicant at a concentration of 100 μg/L, complete suppression of the pathogen is revealed. When the TvV-the SM2 algal virus affects <i>T. viridis</i>, the latent period of infection is 24 h and the rate of algal cell lysis is equal to 2.59 day^–1 on average. Upon contact of the EhV-SS2 algal virus with <i>E. huxleyi</i> culture, the latent period increases 4.2 times and the lysis rate decreases by almost an order of magnitude. During the latent period of infection, a 1.7- to 2-fold decrease in the efficiency of photosystem II is observed in both infected cultures. By the end of the experiments, an average of 10% of algal cells are not lysed.</p>