UPDATE: 8:40 p.m.
The Okanagan Indian Band says an assessment of Okanagan Lake water in the northern arm has found a combination of high organic material including sewage output, grass leaves, burlap, sand and dead animals combined with the high temperatures of the past few days has resulted in an algae bloom.
The OKIB's emergency operations centre will be monitoring the bloom but residents are advised it will be a common sight over the coming days.
Residents and visitors are advised not to go into the water, drink or have contact with the water.
Approximately 200 residences on OKIB land, both seasonal and permanent, remain on evacuation order due to flooding.
ORIGINAL STORY 2:16 p.m.
The Okanagan Indian Band has issued a warning after a raw sewage discharge into the northern end of Okanagan Lake.
"The event has been reported to the Ministry of Environment and is currently under investigation," said an OKIB release on its Facebook page.
The OKIB's emergency operations centre (EOC) has asked residents and visitors "to refrain from entering into the northern arm of Okanagan Lake until further notice."
People have also been warned not to drink the water.
"Sewage water pollution is dangerous, disgusting and filthy dirty. It can be filled with potentially life-threatening hazards," said the release.
The band said Sunday that the lake level is down .4 mm to 343.140 metres.
When the flooding began weeks ago, band chief Byron Louis had expressed concern about waters invading septic fields.
Neighbourhoods on band land have been hit hard by the flooding.