Different types of environments resulting from the dynamic equilibrium between the sea, the river and freshwater can be found in the Baix Ter plain. The interaction between the sea, the river and the sediments it carries has given rise to a wide variety of ecosystems, with very subtle variations in the duration of floods, depth, salinity, nutrient content or type of substrate. The variety of environments and the diversity of organisms that can be found in them are two of the most important ecological aspects of the area. A description of the main aquatic ecosystems found in the Baix Ter follow.


- marshlands and coastal lagoons


- coastal freshwater ponds

Coastal freshwater ponds are located next to the sea but receive freshwater from irrigation ditches. They are, usually, old streams separated from the river but that still carry a sometimes imperceptible amount of water. The Ter Vell and Basses d’en Coll ponds are a good example.
Marine influence is also felt in these ponds. During stormy weather seawater penetrates into the area significantly increasing salinity levels; but after the storm continuous influx of freshwater results in a decrease in salinity levels. Freshwater influx is changes quite a bit because the irrigation ditches are used to irrigate crops and therefore, influx depends more on crop irrigation than on the weather.
Nutrients from fertilisers and other human activities seep into the ponds. They also receive partially (or not at all) purified sewage water. Irregularity in the influx of water, organic matter and nutrients are the main causes the quality of water and the ecological estate of the ponds is not the one desired.

Vegetation profile of the Basses d'en Coll

- springs
- inland temporary ponds
- river Ter estuary
- strongly humanized aquatic atmospheres