1It's quite hard to think of a city that doesn't have a big river running through it.
2If you think about the major cities in the world,
3Shanghai, New York, Mumbai, London,
4they're nearly all built on rivers.
5When these cities were established hundreds or even thousands of years ago,
6the rivers were a big part of people's lives.
7In 16th century London, the quickest way to get from one part of the city to another was by river.
8But people also used the river for fishing as the water then was relatively clean,
9and they would also go on boat trips up and down the river just for pleasure
10as a relaxing escape from the noise and bustle of the city streets.
11But as industries developed and populations increased city rivers suffered.
12The rising number of people meant there was a huge increase in the amount of sewage discharged into the rivers.
13Rivers had always been used for this purpose,
14but when the number of inhabitants was so small, that wasn't such a problem.
15However, as cities grew to over a million inhabitants,
16the impact on the rivers became more serious.
17In addition, other types of pollution increased,
18as factories were built beside the river and discharged their waste materials into the water.
19This got worse over time.
20As recently as 1957,
21scientists at London's Natural History Museum declared that the River Thames was dead in biological terms,
22as the water was too filthy to support any kind of life.
23But in recent years, as rivers lost their industrial function,
24cities have begun to recognise their true value and to take steps to clean them up.
25For example, the River Thames is now cleaner than it's been for 150 years.
26These days you can see seals swimming in the water,
27and recently people had to try to rescue a whale, which had got lost and swam up the river from the sea by mistake.
28Unfortunately, they didn't succeed,
29but the problem was disorientation rather than the quality of the water.
30Then, all around the world, riverside areas are now seen as prime sites for development.
31Warehouses that were once used for storing goods are now being converted into expensive restaurants
32and also into apartments with river views, which are in great demand and sell for astronomical prices.
33In Los Angeles, on the west coast of the USA, an architect has plans to revitalise the banks of the river
34and to make a park there which can provide facilities for sports as well as a natural environment for relaxing in.
35It's also hoped that the riverside can be used for other purposes.
36It's been proposed that facilities could be provided for displaying projects related to various kinds of art
37that have been produced by local people, for example.
38In the city of Paris, during the summer months of July and August,
39all the traffic is banned from the roads by the sides of the river,
40and the banks are transformed into beaches,
41where people can relax in deck chairs under potted palm trees,
42sunbathe or buy a drink or a snack while enjoying the view.
43But to make the most of our rivers in our increasingly crowded cities,
44we need to allow them to regain their original purpose and be used as a means of transport,
45reclaiming our streets from cars and lorries.
46To do this, we'll have to shift more traffic back to the river,
47but this time cleanly and silently, making the most of modern technology.
48Already, more than two billion passengers use the ferry to travel in cities around the world,
49like Istanbul, San Francisco and New York,
50and these numbers are set to rise further.
51Admittedly, it's not a fast way of travelling,
52but neither is a car when it's stuck in traffic.
53Of course, passenger traffic on roads might decrease as more people start working from home,
54but another recent development, the huge rise in online shopping,
55has meant that another form of urban traffic just keeps on growing,
56and that's deliveries.
57Trucks and vans in the city pollute and double-park while dropping off parcels.
58Imagine using the immense capacity of shipping to take these trucks off the road.
59One freight barge can replace 44 large trucks, uses far less energy and causes less pollution.
60When the barge docks at the riverside,
61the parcels could be taken the last few kilometres to their final destination on cargo bikes, electric ones of course.
62This is already happening in the Dutch city of Amsterdam,
63and in future, the final stage could even be carried out by drone,
64although at present this isn't allowed.
65Wouldn't it be great to unblock our city centres in this way?
66Looking further ahead...