Mucilage events may severely affect the benthic fauna and flora in marine environment, likely causing serious mortality in marine life. The present study was made on a massive mucilage phenomenon in the Çanakkale Strait (Dardanelles) and North Aegean Sea in 2021. Blanket type of mucilage existed for five months between March and July in the Çanakkale Strait, impacting marine benthos, which lead to a likely ecological destruction at some locations. Saros Bay, Gökçeada, Bozcaada and Tavşan Islands (Mavriya) were also impacted by this massive mucilage phenomenon. The highest mean thickness of blanket type of mucilage was observed as 16.26±5.97 cm, while the lowest value was measured as 3.5±0.86 cm. Regarding mucilage aggregates-based mortality in marine invertebrates, 77 individuals of the Pennatulacean coral Pteroeides spinosum were found dead. Data of thickness on substratum of mucilage aggreates is reported for the first time in the inventory of the Turkish marine researches.