Tucked away in a mountainous region in southeast Europe is a lake. It’s called Lake Ohrid, and it’s not that big as lakes go, being just 22 1/2 miles long by 10 1/2 wide. There are many more, much larger, areas of freshwater both in this country and scattered throughout the world. It’s not even the deepest lake on earth — that honor lies with Lake Baikal in Russia --but even so, Ohrid is reasonably deep. At its maximum depth, it plunges 945 feet to the lake bed, with an average depth of just over 500 feet.
So, it’s not the biggest nor the deepest lake in the world but Ohrid is one of the oldest, sitting at No. 6 on the list of the world’s most ancient freshwater lakes. It was formed between 3 and 6 million years ago in an area of continuing seismic activity on what is now the border between the states of Albania and North Macedonia.
Lake Ohrid’s particular claim to fame is that it’s been deemed to be a World Heritage Site. This designation has been given due to its ecosystem, which is unique in the world, and which contains more than 200 species that are only found there and nowhere else. It is said to be the most densely biodiverse lake on the planet and many of its endemic species are termed to be “living fossils.”
These differing species cover the whole spectrum of the aquatic food chain, from fish to microscopic plankton. On the floor of the lake there are differing kinds of plants and flatworms, together with unique types of shellfish, crayfish species, snails and even freshwater sponges that cannot be found anywhere else on earth.
There are several reasons why these unusual plants and animals have developed here and have survived through the centuries, while other species have not taken over. The lake gets its water partly from rainfall, but mainly from underground springs and from another lake, Lake Prespa, which lies about 7 miles away. The water from Prespa trickles through the rocks of this mountainous area and brings very little sediment with it, meaning the waters in Ohrid are particularly clear and in places it is possible to see down more than 65 feet. Being fed in this way, the waters of the lake are also low in nutrients, yet they are high in oxygen content and only flora and fauna that could adapt to these conditions have been able to survive and flourish. The lack of nutrients makes it safe for humans to drink water straight from the lake.
There are 17 different species of fish known to live in the lake, and eight of these are found nowhere else in the world. Two of them, the Ohrid trout, called the “Koran” in Albania, and the much smaller Belvica trout, form an important part of the local economy. The people living in the area have fished for, and eaten, the delicate pink flesh of these fish for hundreds of years, but now that source of income, and of protein, is seriously endangered.
Part of the problem was overfishing coupled with the trout’s unique life cycle. Ohrid trout only reach maturity when they are five or six years old and, even then, due to the lack of nutrients, their egg production is less than a fraction of 1% of that of a common carp. In addition, they need water that never exceeds 60 degrees and they rely on the unusually high oxygen content that is found in the lake.
These factors make their breeding conditions fragile, and construction work, plus pollution of the water due to an influx of tourists into the area, together with the over fishing has meant a large fall in the fish population.
As long ago as the 1930s, the falling catches were noted and the Ohrid Hydrobiological Institute was founded. This used a system in which they paid the fishermen to harvest the fish eggs and sperm during the breeding season and mix them together. The Institute would then buy the eggs, hatch them and raise the fish before re-introducing them into the lake.
This system worked well into the 1990s while the communist governments only allowed state companies to fish for strictly controlled amounts of fish. When communism in the area collapsed, however, the overfishing started all over again and began to affect organisms throughout the food chain.
In 2005, it was realized that this was affecting the whole ecosystem of the lake and the World Bank stepped in with funds to refurbish a fish hatchery on the Albanian side of the lake. These days, this facility produces more than a million trout each year while the North Macedonian hatchery puts twice that number back into the lake.
North Macedonia currently has a ban on fishing for the trout, while Albania is trying to enforce a minimum size limit on fish that are caught in its waters. In addition to these efforts, there have been some attempts to introduce the trout elsewhere in the world. During the 1950s, half a million trout were introduced into a lake in Serbia and, although they thrived for a time, spawning did not go well and their current numbers are not known. Our own US Geological Survey has reported that Ohrid trout were stocked by the U.S. Fish and Wildlife Service in three locations — Parvin Lake, Big Creek Reservoir, and Turquoise Lake in Colorado — in the late 1960s. Stock was also introduced to locations in Minnesota, Montana, Tennessee, and several lakes in Wyoming. These trout were brought from the Balkans and were raised at hatcheries in Iowa and Minnesota before being stocked into the various lakes in 1969. So far it appears that none of these stocking attempts have succeeded, although the fish have been restocked several times in Tennessee since then, but so far no sign of natural reproduction has been seen.
The waters of Lake Ohrid are unique. There is nowhere else like it in the world, but its biodiversity is being threatened by human activity. Albania and North Macedonia are not rich countries, yet they appear to be doing their best to preserve the heritage nature has given them. I, for one, wish them luck and hope they get all the support they need to make their efforts successful.