The Blue Lakeis one of the main focuses of Imotski in Croatia. Its access to the constantly changing water level made this karst chasm a place that has been captured forever in people hearths, evoking many nice memories. The Blue lake, a symbol of Imotski and protected natural monument, is a typical karst lake. The lake is inclined from the north to the south. The lake is very deep. The bottom of the lake can be reached by serpentines. It is a popular place for tourists and Imotski residents who like to take walks to the main vista and back to the town, often several times per day. It is very accessible. There are several man made vistas in the lake offering beautiful views. Spending a few hours exploring it is highly recommended.
From the standpoint of the hydrography of limestone regions, the Blue Lake is very interesting and instructive indeed. A long and important line of tectonic disturbance seem to extend from Ljubuški over rude and along to the north-eastern border of the “polje” o Imotski towards Buško Blato. Along that line there is a number of hydrogeologic phenomena: springs, sinkholes. Among them are the springs of the river Vrlika at the altitude of 268 m above the sea, and a number of young “ponikvas”, not yet filled up and containing water. These are known as the lakes of Imotski. All of them are in Dalmatia, close to the border of Hercegovina, and along the border of the “polje” of Imotski. One of them is the Blue Lake.
Except the run-off from their geographic drainage areas, which are extremely small, the Blue Lake receives and loses water only subterraneously. Since the Blue Lake reaches an altitude of 342 m, it must receive water from sources higher than that, but could be fed, in addition, also by lower sources. The lake is in upper-cretaceous limestones that lie on dolomite. The subterranean watercourses, at the contact of limestone and dolomite, corroded the limestone and eroded the dolomite so far the ceiling of the large cavity successively collapsed. The contact of water in the lake with both limestone and dolomite is confirmed by the percentage of magnesium hardness in total hardness. The lake shows homogeneous water from top to bottom, its hardness increasing with depth, as is usual, but with all characteristics nearly constant in hypolimnion. It shows thermal stratification with well-expressed epi-, meta- and hypolimnion. The overturn may occur at temperatures higher than 4.0 °C, as is shown by bottom temperature of the lake; in that case, the lake would be monomictic. The lake is holomictic. In the lake there were found only few microorganisms and bacteria.
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Main analytical data on the Blue Lake – depth 0 m
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Hardness
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% of Mg-hardness
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total
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carb.
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Mg
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163
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145
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26
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16,1
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Main analytical data on the Blue Lake – depth 34 m
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Hardness
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% of Mg-hardness
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total
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carb.
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Mg
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178
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160
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30
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16,9
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Observed elevations above see:
MAX MIN
283,6 m 239,0 m
1. Describe the shape of Blue Lake
2. What is the Croatian name of Blue Lake?
3. When and why can water depth reach or exceed 90 meters?
Please attach your photo at the location (see the spoiler).
E-mail your answers via the profile; subject: „Blue Lake“.
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