Judarn is the name of a small lake in Bromma, a western suburb in Stockholm

Stockholm

Stockholm is the capital and the largest city of Sweden and constitutes the most populated urban area in Scandinavia. Stockholm is the most populous city in Sweden, with a population of 851,155 in the municipality , 1.37 million in the urban area , and around 2.1 million in the metropolitan area...

, Sweden

Sweden

Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....

. Surrounded by the forest and nature reserve Judarskogen, it stretches between Åkeshov and Södra Ängby

Södra Ängby

Södra Ängby is a residential area blending functionalism with garden city ideals, located in western Stockholm, Sweden, forming part of the Bromma borough....

. Three other lakes are found nearby: Kyrksjön

Kyrksjön

Kyrksjön is a small lake in Bromma, a western suburb in Stockholm, Sweden. Named after its vicinity to the old church Bromma kyrka, the lake was made part of the nature reserve Kyrksjölöten in 1997...

, Lillsjön, and Råcksta Träsk

Råcksta Träsk

Råcksta Träsk is a small lake in the western suburbs of Stockholm, Sweden. Notwithstanding its location in the vicinity of the Swedish capital and high levels of lead and copper, the lake is considered as an important breeding ground for frogs, of moderate interest to pleasure fishing, and of...

. The name is etymologically

Etymology

Etymology is the study of the history of words, their origins, and how their form and meaning have changed over time.For languages with a long written history, etymologists make use of texts in these languages and texts about the languages to gather knowledge about how words were used during...

 associated to ljuda, the verb "to sound".

Characteristics

With an area of 74,000 square metres and an average depth of 2.7 metres (maximum 3.7 m), the lake contains 180,000 cubic metres of water and is supplied by a drainage area of 0.8 km². Originally supplying lake Lillsjön, Judarn today discharges into lake Mälaren

Mälaren

Lake Mälaren is the third-largest lake in Sweden, after Lakes Vänern and Vättern. Its area is 1,140 km² and its greatest depth is 64 m. Mälaren spans 120 kilometers from east to west...

. Regarded as one of the least contaminated lakes in Stockholm, Judarn receives storm water

Stormwater

Stormwater is water that originates during precipitation events. It may also be used to apply to water that originates with snowmelt that enters the stormwater system...

 from a nearby traffic route which gives it considerable levels of lead

Lead

Lead is a main-group element in the carbon group with the symbol Pb and atomic number 82. Lead is a soft, malleable poor metal. It is also counted as one of the heavy metals. Metallic lead has a bluish-white color after being freshly cut, but it soon tarnishes to a dull grayish color when exposed...

 resulting in a bathing ban, metal content otherwise being low and phosphorus

Phosphorus

Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...

 levels moderate. The lake, considered as being of great recreational and natural value, is part of the nature reserve Judarskogen and has a rich flora and fauna with many aquatic plant

Aquatic plant

Aquatic plants are plants that have adapted to living in aquatic environments. They are also referred to as hydrophytes or aquatic macrophytes. These plants require special adaptations for living submerged in water, or at the water's surface. Aquatic plants can only grow in water or in soil that is...

s, bird

Bird

Birds are feathered, winged, bipedal, endothermic , egg-laying, vertebrate animals. Around 10,000 living species and 188 families makes them the most speciose class of tetrapod vertebrates. They inhabit ecosystems across the globe, from the Arctic to the Antarctic. Extant birds range in size from...

s, and frog

Frog

Frogs are amphibians in the order Anura , formerly referred to as Salientia . Most frogs are characterized by a short body, webbed digits , protruding eyes and the absence of a tail...

s. Its isolated location combined with low levels of chlorophyll

Chlorophyll

Chlorophyll is a green pigment found in almost all plants, algae, and cyanobacteria. Its name is derived from the Greek words χλωρος, chloros and φύλλον, phyllon . Chlorophyll is an extremely important biomolecule, critical in photosynthesis, which allows plants to obtain energy from light...

 makes Judarn one of the clearest lakes in Stockholm, and notwithstanding low levels of oxygen

Oxygen

Oxygen is the element with atomic number 8 and represented by the symbol O. Its name derives from the Greek roots ὀξύς and -γενής , because at the time of naming, it was mistakenly thought that all acids required oxygen in their composition...

 nutrient content is low even during winters, with raised levels of PAH

Polycyclic aromatic hydrocarbon

Polycyclic aromatic hydrocarbons , also known as poly-aromatic hydrocarbons or polynuclear aromatic hydrocarbons, are potent atmospheric pollutants that consist of fused aromatic rings and do not contain heteroatoms or carry substituents. Naphthalene is the simplest example of a PAH...

 and PCB

Polychlorinated biphenyl

Polychlorinated biphenyls are a class of organic compounds with 2 to 10 chlorine atoms attached to biphenyl, which is a molecule composed of two benzene rings. The chemical formula for PCBs is C12H10-xClx...

 in deep sediments.

Geology

Geological traces of the inland ice

Ice sheet

An ice sheet is a mass of glacier ice that covers surrounding terrain and is greater than 50,000 km² , thus also known as continental glacier...

 which withdrew from the area some 11,000 years ago are found in the moraine

Moraine

A moraine is any glacially formed accumulation of unconsolidated glacial debris which can occur in currently glaciated and formerly glaciated regions, such as those areas acted upon by a past glacial maximum. This debris may have been plucked off a valley floor as a glacier advanced or it may have...

s around the lake. The huge square blocks of stone scattered in the area are the result of the earthquakes produced by the tension caused by the retiring ice. The geologist Gerhard de Geer studied the surrounding moraine ridges, which were eventually given his name, and geological excursions are still common in the area.

Flora

The flora in the lake itself is reduced to a few species, including White Waterlily

Nymphaea alba

Nymphaea alba, also known as the European White Waterlily, White Lotus, or Nenuphar, is an aquatic flowering plant of the family Nymphaeaceae....

, Common Bladderwort

Utricularia vulgaris

Utricularia vulgaris is an aquatic species of bladderwort found in Asia and Europe. The plant is a free-floating and does not put down roots. Stems can attain lengths of over one metre in a single growing season, but die back and form turions in winter...

, and Whorled Water-Milfoil

Myriophyllum

Myriophyllum is a genus of about 69 species of freshwater aquatic plants, with a cosmopolitan distribution. The center of diversity for Myriophyllum is Australia with 43 recognized species...

; while others plants are found along the beaches, including Narrow Leaf Cattail

Typha

Typha is a genus of about eleven species of monocotyledonous flowering plants in the family Typhaceae. The genus has a largely Northern Hemisphere distribution, but is essentially cosmopolitan, being found in a variety of wetland habitats...

, Slender Tufted-sedge

Carex

Carex is a genus of plants in the family Cyperaceae, commonly known as sedges. Other members of the Cyperaceae family are also called sedges, however those of genus Carex may be called "true" sedges, and it is the most species-rich genus in the family. The study of Carex is known as...

, Greater Pond-sedge

Carex

Carex is a genus of plants in the family Cyperaceae, commonly known as sedges. Other members of the Cyperaceae family are also called sedges, however those of genus Carex may be called "true" sedges, and it is the most species-rich genus in the family. The study of Carex is known as...

, Marsh Cinquefoil

Potentilla

Potentilla is the genus of typical cinquefoils, containing about 500 species of annual, biennial and perennial herbs in the rose family Rosaceae. They are generally Holarctic in distribution, though some may even be found in montane biomes of the New Guinea Highlands...

, Gypsywort, Yellow loosestrife

Lysimachia

Lysimachia is a genus of flowering plants. It is traditionally classified in the family Primulaceae but should, according to molecular phylogenetic study, be placed to the family Myrsinaceae .-Characteristics:...

, Purple Loosestrife

Purple loosestrife

Lythrum salicaria is a flowering plant belonging to the family Lythraceae, native to Europe, Asia, northwest Africa, and southeastern Australia. It should not be confused with other plants sharing the name loosestrife that are members of the family Primulaceae...

, and Corn Mint

Mentha arvensis

Mentha arvensis is a species of mint with a circumboreal distribution. It is native to the temperate regions of Europe and western and central Asia, east to the Himalaya and eastern Siberia, and North America.It is a herbaceous perennial plant growing to 10–60 cm tall...

. An isolated biotope

Biotope

Biotope is an area of uniform environmental conditions providing a living place for a specific assemblage of plants and animals. Biotope is almost synonymous with the term habitat, but while the subject of a habitat is a species or a population, the subject of a biotope is a biological community.It...

 of Greater spearwort

Ranunculus

Ranunculus is a large genus of about 600 species of plants in the Ranunculaceae. Members of the genus include the buttercups, spearworts, water crowfoots and the lesser celandine....

 is found on the southern end of the lake. Among surrounding trees and bushes can be found Black Alder

Black Alder

Alnus glutinosa is an alder native to most of Europe, including all of the British Isles and Fennoscandia and locally in southwest Asia....

, Buckthorn

Buckthorn

The Buckthorns are a genus of about 100 species of shrubs or small trees from 1-10 m tall , in the buckthorn family Rhamnaceae...

, Grey Sallow

Grey Sallow

Salix cinerea is a species of willow native to Europe and western Asia.It is a deciduous shrub or small tree growing to 4-15 m high. The leaves are spirally arranged, 2–9 cm long and 1–3 cm broad , green above, hairy below, with a crenate margin...

, and Bay Willow

Bay Willow

Salix pentandra is a species of willow native to northern Europe and northern Asia.It is a large shrub or small tree growing to 14 m tall , usually growing in wet, boggy ground. The leaves are glossy dark green, 5-12 cm long and 2-5 cm broad, with a finely serrated margin...

.

Fauna

The fauna is dominated by Gastropods, Caddisflies

Trichoptera

The caddisflies are an order, Trichoptera, of insects with approximately 12,000 described species. Also called sedge-flies or rail-flies, they are small moth-like insects having two pairs of hairy membranous wings...

 and dragonflies

Odonata

Odonata is an order of insects, encompassing dragonflies and damselflies . The word dragonfly is also sometimes used to refer to all Odonata, but the back-formation odonate is a more correct English name for the group as a whole...

. Fishes present in the lake include Perch

Perch

Perch is a common name for fish of the genus Perca, freshwater gamefish belonging to the family Percidae. The perch, of which there are three species in different geographical areas, lend their name to a large order of vertebrates: the Perciformes, from the Greek perke meaning spotted, and the...

, Roach

Rutilus

Rutilus is a genus of fishes in the family Cyprinidae, commonly called roaches. Locally, the name "roach" without any further qualifiers is also used for particular species, particularly the Common Roach Rutilus (Latin for "shining, red, golden, auburn") is a genus of fishes in the family...

, and Crucian carp

Crucian carp

The crucian carp is a member of the family Cyprinidae, which includes many other fish, such as the common carp, or the smaller minnows. They inhabit lakes, ponds, and slow-moving rivers throughout Europe and Asia. The crucian is a medium-sized cyprinid, which rarely exceeds a weight of over 3.3...

. Mirror Carp

Common carp

The Common carp is a widespread freshwater fish of eutrophic waters in lakes and large rivers in Europe and Asia. The wild populations are considered vulnerable to extinction, but the species has also been domesticated and introduced into environments worldwide, and is often considered an invasive...

 and Signal crayfish

Signal crayfish

The signal crayfish, Pacifastacus leniusculus, is a North American species of crayfish. It was introduced to Europe in the 1960s to supplement the Scandinavian Astacus astacus fisheries, which were being damaged by crayfish plague, but the imports turned out to be a carrier of that disease...

 have been introduced in the lake, the crayfish forming a population allowing fishing. A population of Great Crested Newt

Great Crested Newt

The Great Crested Newt, also called Northern Crested Newt or Warty Newt is a newt in the family Salamandridae, found across Europe and parts of Asia.-Distribution:...

 has now vanished, but the City of Stockholm is planning to reintroduce them by constructing dams and ponds to recreate their natural habitat.

Visiting

Walks around the lake are organized regularly by Bromma borough

Bromma borough

Bromma is a so called borough in the western part of Stockholm, Sweden, forming part of the Stockholm Municipality. Bromma is primarily made up of the parish with the same name, and the parish of Västerled...

 and the Society for Nature Conservation (Svenska Naturskyddsföreningen). Nearest metro station is Åkeshov.