Location
The Druzno Lakie is located in south-eastern part of Zulawy Elblaskie (the Elblaskie Marshlands). It is a remnant of old Zalew Wislany (Vistula River Lagoon), which it used to be a part of. It is shallow, located below sea level, it lies in depression about 0.5 m. below sea level.

Special value
Ecosystem of the Druzno Lake is unique. The lake is very shallow (0.8 m), wide, strongly eutrophized with strong water level fluctuation. Three is a wide variety of biotopes - from breeding forests, through alder swamp and rushes, to strips of floating and immersed plants. This is a place where 110 species of birds nest and a resting point on migration routes of another 100 species. Inaccessible, marshy shores are an excellent shelter and a breeding place for birds.

Landscape and climate
Landscape of the lake is diverse. Forests and bushes dominate on the shores, then they gradually develop into reed belts and rushes. Vast areas are overgrown with varied vegetation. Among cattails and reeds white and yellow water lilies float on water, as well as yellow floating hearts - very rare in Poland, but quite common here. The picture is completed by great number of birds. Chirp, quacking and all different kind of sounds come from thicket of rush, surface of the water and from the air.

The climate is characterized by high humidity, though amount of rainfall is relatively small. The lake lies on the area influenced by the masses of continental and sea air. This is why winters are mild and summers moderate. Although Zulawy Elblaskie area lies within the coldest region of our country - Warmia and Mazury - winters are not dramatically cold because of the influence from the nearby sea. Strong air currents occur around the lake. Wide open area with no forests does not slow down winds, thus sometimes the Druzno Lake is very windy. Snow cover lies here for about 60 days. The heaviest rainfalls appear during summer months - from July to August.

Ecosystem
Ecosystem of the lake is very rich. Yellow and white water lilies have been observed here. Yellow floating heart, very rare in Poland, occur here in many clusters and still expands. Large areas are occupied by rigid hornwort and whorled water milfoil. On the eastern shore the water soldier holds guard. On the outer edge of reed strip hedge bindweed, common ladyfern, skullcap, gypsywort, fen ragwort, and climbing nightshade occur.

Shores of the lake are overgrown with (among others): common reed, narrow leaf cattail and common cattail, bur-reed and sedges.

Within the Druzno Lake area one can distinguish four types of communities (Karczewski 1953).

1. Young quagmires: lush, vast reed fields with clusters of yellow and white water lilies as well as narrow leaf cattail. There is environment of birds: bearded tit, woodstar, mute swan, ferruginous duck and grebes - red-necked and great crested.
2. Old quagmires bordering on the lake. Flooded for most of a year, with many clusters of grey willow. There are also few communities of high sedges and common cattail. Here also dwell: penduline tits, bitterns, scarlet rosenfiches, water rails, spotted crakes.
3. Clusters and scrubs of trees and bushes growing closer to mainland. Here reigns black alder and white willow. Many open spaces are overgrown with communities of high sedges. It is a habitat of grashopper warbler, bluethroat and crane.
4. Bays dominated by water soldier, overgrown in forelands by white and yellow lilies. In the back deep quagmires with seagulls, eared grebe.

The described communities are habitats for many other bird species. Recorded among others are: black-headed gulls, four species of terns, including white-winged black tern and whiskered tern, greylag geese, ducks, gadwalls, garganeys, tufted ducks and pochards, white-tailed eagle, marsh harrier, common buzzard, goshawk. In reeds: reed warbler, sedge warbler, bearded tit. In bushes and coastal forests: vinaceous rosefinch, lesser spotted woodpecker and black woodpecker, redwing.

In the lake's water swim crucians, tenches, breams, perches, eels and luces. Over the water fly dragonflies and other insects and in coastal forests with great luck we can spot a goose or a roe deer, a fox, a raccoon dog, an ermine, an otter and a stone marten. At dusk bats appear in the sky. Among them there are brown long-eared bat and common pipstrelle.

Threats
One of the threats to the lake is the natural process of overgrowing. Another serious threat is polluting the lake with wastes of agricultural, communal and industrial origin. Also dangerous are hunting in the reserve's close vicinity and intensive fish poaching.

Environmental protection
The whole area of the lake has been taken under protection as a strict nature reserve. In order to protect hatching places of water birds as well as for the landscape's sake on 29th of December 1966 by the disposition no.179 of the Minister of Forestry and Wood Industry the Druzno Lake Reserve was established. It encompasses the Druzno Lake together with boggy lands and forests around it. The area of the reserve is 3021.6 ha.