Blatina kraj Sobre, Protected natural site on Mljet island, Croatia.

Blatina kraj Sobre is a protected natural site on Mljet island composed of several habitat types with Mediterranean plant life. The landscape includes open areas, dense scrubland, and forested sections that together form an interconnected ecosystem.

The site gained official protection status in 2013 as part of efforts to safeguard its natural habitats and wildlife. This designation connected it to a broader network of protected areas across Croatia's coastal regions.

The lake's two submerged karst funnels are named Jaz and Struga, and the site's name, Blatina kraj Sobre, refers to the muddy pool by Sobre. The brackish water is drawn through a desalination plant to supply drinking water for the whole island of Mljet, so the protected area is also the island's water source.

Access is by ferry to Mljet island followed by walking along marked pathways through the natural area. The warmer months offer the best visiting conditions when trails are easy to walk and weather is stable.

Below the surface, at the centre of the lake, lie two funnel-shaped karst caves called Jaz and Struga. The lake's brackish water is drawn on to supply drinking water for the whole island of Mljet through a desalination plant. The water level itself swings from about 0.5 m in summer to 5 m in winter.