China saw 24 red tides in its coastal waters in the first six months this year, with a total contaminated maritime area of 982 square km, according to a report released by the State Oceanic Administration (SOA).

It was less than the average number of red tides for the same period over the last five years, the administration said Thursday.

During the January to June period, 14 red tides occurred in the East China Sea with a total contaminated sea area of 721 square km, and three red tides were reported in the Bohai Sea, which affected a total sea area of 200 square km, the administration said.

Meanwhile, the South China Sea recorded six red tides in which the affected maritime area amounted to 41 square km, and the Yellow Sea saw one red tide, with a total affected sea area of 20 square km.

In addition, one green tide occurred in the Yellow Sea during the first half of this year, which currently remains there, according the SOA.

A red or green tide, also known as an algal bloom, is when algae accumulate rapidly in water, resulting in discoloration of the surface water. These algae vary in color from green to brown, but are mostly red.