Isel (river)

Geology

The Isel fault trends NW-SE and runs along the Isel Valley. It is related to the lateral extrusion about 17 million years ago that exposed the Hohe Tauern window. The Isel fault cuts the E-W trending Defereggen–Anthois–Vals fault.

There are Quaternary sediments in the Isel Valley, mostly till from the Last Glacial Maximum (LGM) between 23,000 and 19,000 years ago. At that time the valley was filled with an ice stream with its surface about 2,300 metres (7,500 ft) above sea level. The valley from elevations of about 1,700 metres (5,600 ft) down to the valley floor near the Daberbach and Gossenbach tributaries at 720 metres (2,360 ft) often holds coarse-grained, poorly sorted and unconsolidated gravel. These deposits seem to be kame terraces formed by streams of meltwater as the ice stream collapsed after the LGM. By 18,000 years ago the lower Isel valley at Ainet was probably free of ice. A series of terminal moraines were left as the local glaciers retreated during the Late Glacial Interstadial.

Conservation struggle

Planning began in 1971 to create a large reservoir in East Tirol for hydroelectric power generation. All the glacier streams of the region would be diverted into the reservoir. Wolfgang Retter founded the "Association for the Protection of the Recreational Landscape in East Tirol" to fight the plan. The power plant project was cancelled in 1989. In 1998 the Austrian Ministry of Agriculture and Environment and WWF Austria designated the most valuable 74 rivers in Austria as "river sanctuaries". The Ministry and WWF jointly committed to protect the rivers.

On 25 February 2011 a joint meeting of the local councils of Virgen and Prägraten saw a presentation by the Innsbruck company "Infra Project Development GmbH". The company proposed to dam the upper Isel above Hinterbichl in Prägraten and then lead it through a 12 kilometres (7.5 mi) tunnel to a power house in Unterpellach in Mitteldorf / Virgen. The municipalities would pay an estimated seven million euros for construction, then would receive 400,000 euros revenue each year. The meeting was supposed to be private, but details leaked out almost immediately. In November 2011 the municipal council in Matrei was shown a proposal to build a hydropower plant in Huben using water diverted from the Isel, with estimated cost of 55 million euros.

In June 2012 a referendum was held in the Virgental asking "Should the community participate in the planning, construction and operation of an environmentally friendly power plant on the upper Isel?". Voter turnout was high, with 73.9% in Virgen and 79.4% in Prägraten. About 60% or respondents answered "yes" in Prägraten and 72% answered "yes" in Virgen. In September 2012 WWF declared that the Isel was a "National River sanctuary" due to renewed concerns about plans for large power plants in the Isel basin. The proposed project in Virgental would affect 15 kilometres (9.3 mi) of the river and generate 130 GWH of electricity.

In June 2015 the Tyrolean provincial government decided to nominate almost the entire Isel and almost all its tributaries as a Natura 2000 area. This would cover the entire course of the river from the Umbal Falls to the Lienz city limits, and the upper reaches of the Schwarzach and the Kalser Bach. The Natura 2000 zoning would apply to the river only. It would not include cycle paths, roads and sports fields, and landowners would not be displaced. It was not clear that a power plant would be ruled out as long as the habitat was preserved.

Rafting

The river provides good conditions for rafting, with class III and IV rapids. The best conditions are between May and September. The Dolomitenmann extreme sports relay race includes a difficult white water section on the Isel.

Trail

In 2020 the 75 kilometres (47 mi) Isel Trail was opened to the public, leading from the town of Lienz up the Isel valley to the Umbalkees glacier. The upper part of the trail crosses wide alpine grasslands below the Umbalkees ice front, from which the Isel emerges to start its journey down to the Drava. The Upper Umbal Falls, where large volumes of water plunge over a series of steps, are visible at a distance from the trail. The Lower Umbal Falls were opened for visitors in 1976, and have platforms that let visitors view them from close up. The river bed here is smooth rock with washed-out hollows carved by the force of the water. There is another waterfall near Ströden, visible from the bridge.

Near Hinterbichl / Ströden the Glo Gorge is a crevice with almost vertical sides through which the Isel plunges down two large steps throwing huge amounts of spray into the air, often creating a rainbow in late afternoon. Between Welzelach and Bobojach there is a large gorge with a series of cataracts running between steep cliffs. Some of the trees in the canyon are several centuries old. There is a deep gorge below Virgen, with the lowest of the large waterfalls, a series of steps several meters high. The steep sides of the gorge hold relatively undisturbed forest with trees of all ages.

Near Feld the Isel valley narrows and the river is fast-moving and turbulent, running between wide banks of gravel. The cataracts here move large boulders downstream. The Daberer Waterfall is near the mountain village of Schlaiten surrounded by old trees, moss and rich undergrowth. At times of high water flow the waterfall creates a fine mist. On the slower-moving lower Isel between Huben and Lienz there are islands populated by tamarisk, with pinkish-white flowers from May to August.