| Alvajärvi | |
|---|---|
 Southern end of Alvajärvi | |
| Location | Jyväskylä |
| Coordinates | 62°18′50″N25°43′12″E / 62.314°N 25.720°E /62.314; 25.720 |
| Primary outflows | Pappilanjoki |
| Basin countries | Finland |
| Max. length | 4 km (2.5 mi) |
| Surface area | 211 ha (520 acres) |
| Average depth | 3.8 m (12 ft) |
| Max. depth | 16.5 m (54 ft) |
| Water volume | 7.1 million cubic meters (250×10 |
| Residence time | 30 days[1] |
| Shore length1 | 13.6 km (8.5 mi)[2] |
| Surface elevation | 94.9 m (311 ft) |
| Islands | 4[2] |
 Interactive map of Alvajärvi | |
| 1 Shore length isnot a well-defined measure. | |
Alvajärvi[a] is a lake inJyväskylä,Finland, covering an area of 211 hectares (520 acres). It lies between the urban area ofPalokka in the south and the village ofPuuppola in the north. The lake's outflow is the river Pappilanjoki, which flows into lakePalokkajärvi.
The name of Alvajärvi was first attested in 1554 asAlueierffuij. Based on older forms beginning withAlve- instead ofAlva-, linguistViljo Nissilä [fi] has compared the name to the wordsalve meaningfish tapeworm andalvejuuri referring to a species of fern[b] that has traditionally been used to treat intestinal worms. Alvajärvi shares its name withanother lake anda village on its northern shore, located inPihtipudas in northern Central Finland.[4]
Alvajärvi is about 4 kilometers (2.5 mi) long[5] and covers an area of 211 hectares (520 acres).[6] It is located in the northern part of Jyväskylä, between the urban area ofPalokka and the village ofPuuppola. Residential areas by the lake include Kirri, Piilola, Ollila and Heikkilä in the south as well as Matinmäki and Perä-Palokka in the north. TheFinnish national road 4 runs near the lake's western shore.[7] There are four islands in the lake, three of which are small islets in its northern part.[2] The biggest island in the lake is called Lammassaari.[5]
Alvajärvi has a volume of 7.1 million cubic meters (250×10^6 cu ft), its average depth is 3.8 meters (12 ft) and the maximum depth is 16.5 meters (54 ft).[1] The deepest point lies in the middle of the lake, west of the Pilliniemi cape.[7]
Alvajärvi is part of theKymijoki main catchment area and its subordinatePäijänne basin.[8] The lake's own catchment area covers an area of 256 square kilometers (99 sq mi). The main inflow of Alvajärvi is the river Laahajoki, which begins fromKorttajärvi, drains a basin of 236 square kilometers (91 sq mi) and discharges into the northern end of the lake. Another inflow, discharging into the lake's eastern part, is the Karhupuro, with a basin covering an area of 9.54 square kilometers (3.68 sq mi).[2] Due to the long and narrow shape of the lake, it retains water for quite long.[9] Thelake retention time of Alvajärvi is estimated to be 30 days.[1]
Alvajärvi itself discharges into lakePalokkajärvi via the 947-meter (3,107 ft) river Pappilanjoki.[2] Both lakes have approximately the same surface level at 94.8 meters (311 ft)above sea level.[7] The levels of both Alvajärvi and Palokkajärvi, as well as those of Korttajärvi andTuomiojärvi, are regulated by a dam in the riverTourujoki, the outflow of Palokkajärvi.[10]
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According to measurements from 2021, based on samples taken from a meter below surface level, the water of the lake had a pH of 7, a nitrogen level of 740 μg/l (4.3×10−7 oz/cu in), a phosphorus level of 29 μg/l (1.7×10−8 oz/cu in) and aturbidity level of 4,8 FNU.[11] Alvajärvi and Palokkajärvi are very similar in terms of water quality, though the former has slightly darker water and a slightly higherchemical oxygen demand due to runoffs from agriculture.[6] Approximately half of all phosphorus loading in Alvajärvi originates from agriculture, with the highest amount coming from the Makkarajoki basin.[1]
Until the 1970s, wastewater fromTikkakoski was discharged into the riverAutiojoki flowing into Korttajärvi, resulting innutrient loading in both lakes. While phosphorus and chlorophyll levels have decreased since then, the lower layers of both lakes are still occasionally lacking in oxygen, especially in late summer.[1]
Based on data collected in 2010, fish found in the lake includeperch,pike,ruffe,European bullhead,zander,smelt,common bream,burbot,white bream,bleak,common rudd,roach andcrucian carp. TheEuropean river lamprey has also been encountered. In 2009, there were 106 households who had fished on the lake using rods, nets and traps. The total amount of fish caught was 1,708 kilograms (3,765 lb), equivalent to 8.5 kg/ha (7.6 lb/acre) in one year. The most common catches were pike (caught by 25% of fishers), common bream (23%), perch (22%) and zander (22%). Zander have also beenstocked into Alvajärvi, with 12,000 juvenile fish introduced between 2012 and 2015.[6]
The shallow northern bay of Alvajärvi is a locally significant resting place for migratory waterbirds, as ice in the bay begins to melt earlier in the spring than in other parts of the lake due to the Laahajoki discharging there. In the summer, the bay is covered by horsetails and other aquatic plants. Nesting bird species includeblack-headed gulls andlittle gulls.[12] Colonies of black-headed gulls andcommon gulls are also found on and around Lammassaari.[5]