How floating islands can make urban waterways green and clean

(CNN)Many of the world's cities are built around waterways. Paris and the Seine, Allahabad, India and the Ganges, Cairo and the Nile -- these rivers, at one time the life-force of their city, are now so polluted they're unfit for swimming and host very little natural wildlife.

After a year and a half of highly restricted movement, many people have been confined to the gray spaces of the inner city with little opportunity to escape to the countryside. A report published in April found that frequent visits to nature improved psychological well-being and reduced mental distress. No