In rural Tanzania, recent major influences happen between Kiswahili and English to ethnic languages rather than ethnic languages, which had been in contact for so long, influencing each other. In this work, I report the results of investigation of lexical changes in indigenous languages that aimed at examining how ethnic communities and their languages, namely Cushitic Iraqw, Nilotic Datooga, Nyilamba Bantu, Isanzu Bantu, Sukuma Bantu, and (Isolate) Hadzabe, have influenced one another due to contact in Yaeda Chini, Mang’ola, and Endamaghang wards (i.e., Lake Eyasi area). Though they have been in contact for many decades, this study found that ethnic languages in the area have been affected mainly by Kiswahili. It was revealed that loanwords of this official language tend to outnumber loanwords in each language which come from other ethnic languages. It is supported that, in terms of cultural superiority to date, Iraqw and Datooga are far ahead because Iraqw and Datooga languages tend to influence Nyisanzu, Nyilamba, and Hadzabe languages in Lake Eyasi area.