Pro-migrant NGOs working at asylum centres on the Greek islands in the Aegean are calling for the government to release the migrants to the mainland citing poor conditions and overcrowding in the asylum camps.

Nineteen different NGOs have written and delivered a letter to Greek Prime Minister Alexis Tsipras asking the government to end the internment of migrants on the islands of Lesbos, Chios, and Samos. The letter calls for the migrants to be allowed to travel to the mainland of Greece for better quality accommodation, Der Standard reports.

Previous reports have shown that far more migrants are arriving in Greece from Turkey than are sent back to Turkey through the European Union-Turkey migrant agreement. The influx has led to the severe overcrowding of many migrant reception areas like on the islands of Lesbos and Samos where camps designated for only 3,000 migrants now hold over 8,000.

Some of the migrants living in the camps have been there for over a year and a half and the crowding and poor sanitary conditions have led to many riots and other problems on the islands.

Turkey Accused of 'Dissolving' Camps as Migrants Flood Greece https://t.co/QSjmLuCBZW pic.twitter.com/nxipSAYDvx — Breitbart London (@BreitbartLondon) December 10, 2016

Earlier this year in July, 35 migrants were arrested by Greek authorities for participating in riots at the Moria camp on Lesbos only eight days after another riot had taken place.

The NGOs say in their letter that the Greek government simply does not have the resources to provide adequate care and conditions for the migrants on the islands and slammed the lack of “solidarity” from other EU member states.

NGOs have also claimed that the number of violent incidents has increased in recent months including migrants attempting self-harm or suicide. They said that some women opt to wear adult diapers at night because they are too afraid of travelling to the communal toilets aline in the dark.

Though the EU-Turkey migrant agreement has slowed down the number of migrants entering Greece, many have questioned how long the agreement will last after the Turkish government’s repeated threats to scrap the deal and send as many as 3,000 migrants a day to Greece.

German historian Hans Peter Schwarz said earlier this year that he believed the next great migrant crisis was not a matter of if, but rather a matter of when. Schwarz said that the EU was “not prepared” for another wave of mass migration.