In 1922, M. Kand and F. Dreyer studied the radioactivity of the curative mud, which at that time was considered to be the main factor causing the therapeutic effect.

In 1957–1959, the Institute of Experimental and Clinical Medicine of the Academy of Sciences of the ESSR studied sea mud in Hiiumaa Island.

In 1985, the ESSR Geology Administration conducted a comprehensive study for the purposes of determining curative mud reserves and quality in Käina Bay.

[4] According to the study on curative mud in Estonia, carried out by the Centre of Excellence in Health Promotion and Rehabilitation (Estonian: Tervisedenduse ja Rehabilitatsiooni Kompetentsikeskus) in 2013–2014, on the basis of a low concentration of heavy metals, the sediments in Käina Bay can be considered the ecologically cleanest in Estonia.

That is understandable, as the bay is located in the Käina Bay-Kassari Landscape Conservation Area, where a number of restrictions (for example, on the use of boat motors) have been imposed.

The lowest lead (Pb) concentrations among five deposits were detected in Käina Bay, where values do not exceed 20 ppm.