Hanoi releases algae to revive Hoan Kiem LakeThe State-owned Hanoi Sewage and Drainage One Member Limited Company said it has released green algae into Hoan Kiem Lake to revive the unique green colour of the lake. Tanks containing green algae, which are being released into Hoan Kiem Lake to revive its iconic green colour. The water with green algae was pumped out of the lake before it was dredged at the end of last year. Early this year, the company conducted the dredging of Hoan Kiem Lake. Hoan Kiem Lake is one of the country’s national heritage sites and top tourist destination with great historical value.