Axios, Loudias and Aliakmonas rivers irrigate the second-largest plain of Greece and they form one of the largest wetland ecosystem.

Aliakmonas is the biggest in length river of Greece. It springs from Grammos and Voio mountains and after travelling for 350 km it flows into the Thermaikos gulf. The flow of the river is regulated by an artificial lake created by a regulatory barrier which receives water from three hydropower dams.

Axios is the second longest river in Greece with a total length of 320 km, of which 76 km are in Greece. It springs from F.Y.R.O.M, but also from the mountain Varnouda in the prefecture of Florina, and discharges into Thermaikos Gulf. Around 95% of the river basin belongs to F.Y.R.O.M. In the beginning of 20th century the estuaries of Axios river were few kilometers southwest of Thessaloniki, threatening to cut the access to the sea port because of the continuous deposition brought to Thermaikos Gulf. The river bed has shifted with technical works in the place that is found today.

The projects began in 1930 and was completed in 1934. The river delta evolved quickly, and an extensive plain was created. However, recent measurements indicate that the reduction of water supply and the provision of solid material resulted in erosion of river delta over the last 30 years (Karageorgis et al 2005).
There are 13 dams along the riverbed, of which twelve are on his tributaries in F.Y.R.O.M. (Poulos et. al. 2000).

Loudias River has a total length of 39 km and an average flow of 20 cubic meters / second. It is an artificial channel that was created early 30s when the work of desiccation the Lake of Giannitsa (or “Lake Loudia”) was completed.

Lake Loudia was originally a saltish lake, but over the centuries has turned into a marsh of freshwater while it received the water from rivers that drain the mountain arc of Pella (Voras, Jena, Pinovo) and the northern mountain Vermio.

Nowadays Loudias is no longer a natural river but a drainage channel designed to carry water from the drainage network of the former Lake of Giannitsa to Thermaikos Gulf.

 

The lagoon of Alyki Kitrous extents to 352 hectares, with maximum depth 1.5 m and is almost cut off from the sea, as the sea water enters from a small channel width of 4 m, in which the flow of seawater is controlled by a small barrier. The use of the lagoon is the storage of sea water to be used in the salt production. The water level and the salinity of the water depend on the ebb and the tide, but also from the operation of pumping stations, rainfall and evaporation (Hailey and Goutner 2002)

In this area we distinguish four different habitats:

1. Free water surface covers approximately 159 hectares and islets to an extent less than 1 hectare (west side).

2. The saltmarshes, with an area of 254 hectares, which are covered by water. Most of them are on the south side and used for the gradual concentration of seawater. The rest area is used for crystallising salt.

3. The area of saltmarshes, where the dominant vegetation is HALOPHYTIC, such as Arthrocnemum fructicosum, A. glaucum, Halocnemum strobilaceum, Salicornia europaea, Halimione portulacoides and Limonium spp.

4. The area with coastal heaths is about 165 hectares and is characterized by sandy substrate. Along the coast there are sand dunes.

The case of the lagoon Kalochori is unique in Greece, as it is a «new» wetland created gradually from the mid-'50s, as a result of ground subsidence caused by overexploitation of water from underground aquifers in conjunction with the loose of the soil (Anastasiadis et al 2004).

Today the lagoon covers an area of 2,260 acres. The depth of the lagoon is 0.5 to 1 meter below the sea. Despite the general deterioration of the lagoon, due to drought, rubbish and waste, is one of the most important areas within the protected area because of the large number waders and water birds gathering here all year long.

The gulf of Thermaikos is a closed, shallow bay on the Northwest Aegean. It receives fresh water from the three major rivers (Axios, Loudias, Aliakmonas), which all together are estimated to drain an area of about 35,000,000 acres. In the recent years there has been noticed a dramatic reduction in the quantity of fresh water that flows into the gulf. Similarly, there is a reduction in the quantity of the transported sediments that are deposited at Thermaikos gulf which is vital to the ecosystem.

After the construction of the dams in Aliakmonas river almost the total of the sediments are retained, resulting in the drastic reduction of the development of the river Delta, the salinization of soils and groundwater, the penetration of salt water (especially during the tide) and the general degradation of wetland ecosystem.

Human activities significantly affect the coastal ecosystem of Thermaikos gulf and its physical development. The construction of dams on major rivers has reduced dramatically the water and the transported sediments, resulting in the decline of the formation river delta because of erosion by the sea, and the salinization of groundwater aquifers (Poulos et.al. 2000).