A blue eye in the karst
The protected source area includes several springs. The three principal ones are Veliko or Cetina spring (commonly known as Glavaš), Vukovića spring and Batića spring. Official management documents describe the source monument as including the first approximately 200 metres of the river course.
Veliko vrilo is also a submerged speleological feature. Published Croatian environmental documentation records exploration to around 150 metres depth. That figure should be understood as an exploration depth, not a simple “lake depth”: the spring is an underwater cave system, not a conventional basin.
The colour changes with light, season, water level and viewing angle. The deep centre can appear nearly black-blue while the margins reveal pale stone through transparent water. The effect is geological before it is photographic.
