Gamma Forests

The Gamma Forest was a location of unknown origin. The girls from there were known as "Gamma Girls". The forests were not known to have ponds, only rivers. It was also neutral towards recruitment for the Church. The people there were known to craft handstitched cloth symbols of devotion called "prayer leaves". These were embroidered with the names of one's children. in the native tongue of the people of the Gamma Forests, as a sign of belief that child would always come home to them.

The first reference to the forests was by Idris as she was dying. She repeatedly told Rory that "The Only Water in the Forest is the River", causing him confusion. Rory recounted the statement to the Doctor, which WAs dismissed at the time as something yet to come. (DW: The Doctor's Wife)

When Lorna Bucket was a child she once met the Doctor there. She recalled that he repeatedly told her to 'run', implying the situation they faced together had been dangerous. She also implied the reason she enlisted was partly because the Doctor's short visit to the forests was the only thing that had ever happened there. Lorna later crafted and gifted a prayer-leaf to Amy Pond, who had recently been separated from her newborn daughter.

Later as Lorna died, the Doctor pretended to recall their adventure there, despite the fact he did not recall Lorna. It was implied the incident has not yet occurred for the Doctor, as he stated he always remembered everyone he encounters.

After Lorna's death, River Song appeared and mentions the Gamma Forests in part of her argument that some of the horrors he faced now was a result of what he had become, that the kidnapping and use of newborn Melody Pond as a weapon against him was a result of the fear he elicited from his enemies. To hammer the argument home, she mentioned that the people of the Gamma Forests define "Doctor" as "Mighty Warrior". This made the Doctor extremely uncomfortable.

As the Doctor confronted River about her identity, she showed him the prayer-leaf Lorna had crafted laying in his crib, translated by the TARDIS. The Doctor quickly realized who River was and vaguely mentioned that he knows the infant's location before rushing off, potentially the Forests given how heavily it was referenced.

Afterwards Amy and Rory confronted River, who prompted them to look at the prayer-leaf, explaining the name was translated this way because "...the only water in the forest is the river." The letters translated the forest's words for Melody Pond to River Song.  It implied a closer history between River and the location, due to her knowledge and her affinity to be commonly known as their translation of her birthname. (DW: A Good Man Goes to War)