The estuary of the river Myrsonas (wetland Messakti) is located about 0.5 km west of the village Gialiskari, west of Evdilos. It is a natural coastal wetland area of 25.5 acres. This is a river with a relatively permanent flow throughout the year and brackish water, that feeds mainly on small farmers scattered along the riverbed.
The supply of fresh water by the wetland is affected by the dam of the artificial Lake Vathes, located about 3 km upstream of the estuary.
The wetland is located within an area declared as a Wetland of Messakti (estuary of Myrsonas). In the wetland, the following types of habitats are found: reedbeds, Mediterranean salt meadows (Juncetalia maritimi) and vegetation dune sclerophyllous shrubs (Cisto-Lavenduletalia).
The wetland has a rich biodiversity of flora and fauna, as well as populations of many protected and endemic species. It presents an ultra-water vegetation of reed and rushes, which dominate throughout its length and oleanders, osier and lentisk. It also hosts a wide variety of birds, reptiles and amphibians.
The activities in the watershed are relatively mild, mainly grazing and cultivation. The major threats to the wetland resulting mainly from these two activities, are overgrazing and the intense irrigation of crops becomes uncontrollably by tires from the riverbed, thereby reducing the water level.
Lately, another intense threat to the habitat is presented, which is the increased tourism during the summer months, since at the end of the estuary, there is a sandy golden beach Messakti, very famous amongst visitors.