By Julian Siddle

媒體英語會帶大家一起學習BBC撰稿人在報道世界大事時常用到的單詞和短語。

背景：波羅的海正面臨5年來最大的海藻瘋長問題。海藻的泛濫不僅對海洋生物的生長造成影響，同時也給對環(huán)境變化亮起了一個指示燈。

Satellite images show the green algae spreading across the Baltic from the coast of Sweden eastwards towards Lithuania and Latvia.

The growth of this algae is a natural event which occurs every summer as temperatures rise.

But it's not just the heat causing a record increase. This has been partly fuelled by agricultural fertilisers, applied on land, which find their way into water systems.

Researchers from the Department of Botany at Sweden's Stockholm University have raised concerns over potentially dangerous chemicals present in the algae, which they say are linked to degenerative brain diseases. They warn against swimming in any areas covered in algae.

Algae is a fairly fragile plant, and although the current bloom in the Baltic Sea covers over 350 thousand square kilometres, it is likely to be broken up by waves and summer storms.

For human health the high summer temperatures being experienced across northern Europe are more of a concern. A heatwave in 2003 killed more than 40 thousand people in the region and this year record temperatures have been reached in many places around the world.