On 6/17/2015, Tepco announced they measured the highest density of all β nuclide (including Sr-90) in seawater outside of Fukushima plant port.
The sampling date was 6/15/2015. The density was 16,000 – 24,000 Bq/m3.
The sampling locations were the North-East, East, and South-East of the exit of the port. Especially in the South-East of the port exit, all β nuclide had always been under detectable level until this time.
The distance of these sampling locations and the port exit is not announced.
The Strontium-90 density has not been reported either.
Source: Fukushima Diary