Lake Egirdir is a tectonic lake with a depth that exceeds 10 meters at only a few points. The karstic nature of the lake bottom allows water movement both in and out. The lake is fed by three streams which usually dry off during the summer. The lake water flows into Kovada Lake through a canal located to the south. The northern parts of the lake are much shallower and the shores are usually covered with reed beds. The water of the lake is used as drinking water in the provinces of Isparta and Egirdir. The main fish species caught in the lake is pike-perch (Stizostedion lucioperca), which was introduced to the lake in 1955.
The lake water is in good quality and can be considered as oligotrophic. The high amount of calcium and especially magnesium found in the water bound with phosphate decreases the amount of available phosphate for plants to grow. Also, this situation results in very restricted breeding place for the fish, which depend on plant beds to spawn. The north part of the lake has more plant cover, due to its being shallow and having a higher amount of nutrients originating from agricultural practices in the region.
Until the mid 1980ís, Lake Egirdir yielded the highest crayfish (Astacus leptodactylus) production in Turkey. An annual mean of 2000-2500 tons of crayfish catch provided 5-6 million dollars of income. Then the crayfish population collapsed and has nearly become extinct since then. The main reason thought to lie behind this decrease is a fungal disease or enormous increase in pike-perch population as a result of overfishing of crayfish. Eight different native fish species have also become extinct with the introduction of pike-perch.