A species of ray-finned fish found only in Israel has been spotted in the center of the Yarkon River, an area the fish had abandoned for years because it was too polluted, the Yarkon River Authority announced on Thursday.

The return of the fish, called the Yarkon bleak, is seen as an encouraging sign about efforts to clean up the Yarkon River, which runs through Tel Aviv and flows to the Mediterranean Sea.

The bleak had been inhabiting the less polluted eastern part of the river when they were placed in the Tel Aviv University aquarium due to fears that part of the river could dry up.

They were recently returned to the river, but have stayed in the eastern section, until now.

There is still some sewage being dumped in the center of the Yarkon, but due to an improved sewage purification process, the water is considerably cleaner than it used to be. The bleak is not the only species recently sighted in the center of the river. Two months ago Yarkon River Authority officials reported that another species of fish, tilapia, has also returned to the central Yarkon.

In 1997 the river was so polluted that when a pedestrian bridge over the river collapsed during the Maccabiah Games, one Australian athlete was killed during the collapse itself and three died because of infections caused by exposure to the polluted water.