Ka nui ake hoki te mānahana oneone nā te mea he iti rawa te tawhiti i waenganui i te mata me te tēpu wai whenua (1–2 m e ai ki ngā āhuatanga oneone me te pāmahana) hei whakawātea i te wai kia hutia ake e te whakaeto, kia iti ai ngā wheketere tote i roto i te wai whenua i runga i ngā tau.