The River Dobra, the longest underground stream, rises at two springs in Gorski Kotar, near Skrad. It sinks into the very heart of Ogulin, Đula's Abyss. This wayward beauty has been harnessed by man twice. Dams have been placed on its flow creating two lakes: Lakes Bukovnik and Lešće for the hydroelectric power plants of Gojak and Lešće.
The River Dobra has one more rarity. Two watermills which are still in use today, and whose old millstones still grind various grains.
The Dobra with its tributaries, especially the Vitunjčic, attracts the lovers of sports angling who want to enrich their collections of fishing trophies with grayling, brook and rainbow trout, chub, barbel, pomfret, huchen and so on.