Below the Kali Aplal the Oelvab continues to flow towards the northeast, where after a few kilometers it merges with two other rivers.

[4] As soon as it reaches the East Timorese Suco Malelat, it forms the border between Indonesia and Timor-Leste.

This arm flows between Oehoso and Manan on the right side and Naktuka on the left, forming more river islands and several tributaries, and also flows into the Sawu Sea a little later[1] The catchment of the Noel Besi River is one of the 18 largest catchments in Timor-Leste,[5] but is not in the top 10.

[7]: 9 Timor-Leste has been broadly divided into twelve 'hydrologic units', groupings of climatologically and physiographically similar and adjacent river catchments.

Now the area of 1,069 hectare has a "free zone" status, cannot be entered by population of both country, although historically, Naktuka belonged to Indonesia, according to the agreement between Portugal and the Netherlands in 1904.

[13] In 2017, 63 families from Timor-Leste occupied Naktuka, with immigration office, church, electric network and meeting place of the Oecusse people.

[13] Indonesia wants the Noel Besi as its area according to toponym, whereas Timor-Leste wants the Nono Nomna River based on compass azimuth.