How can I fix pollution?

There is no (official) evidence yet that ground pollution can be removed. However, some users reported that pollution might disappear after a while. Still, other sources report that removing ground pollution isn't possible. You can remove any water pollution by placing water recycling plants which are unlocked at a population of 16.000. It will take some time then, but your water pollution will fade away.

You can always change your industry to forestry or agricultural to reduce ground pollution. Place your industry and pollutive buildings far away from your residential area to increase the global health.

It seems like you have an ordinary (generic) industry complex in your city, at least that's what I see on your screenshot. That's not unusual.

The water pollution should be easily solved: place your sewage things downstream from the fresh water things, that way they won't take in polluted water. This is the only cause of water pollution that I have come across so far.

As to the other pollution there are two types left: noise and ground. One major cause of ground/noise pollution is industry which has an equally straightforward solution: separate it from your residential areas so the suburban society doesn't complain.

Some other things like airports, trainstations and dump yards also cause these so you should consider putting them on the outskirts of cities and preferably with a buffer zone between residential areas.

On Skylineswiki there is a note that says

Pollution can be decreased by planting trees in polluted areas. And sound pollution produced by roads can be lowered by upgrading them; sound barriers for motorways, and trees for normal roads. Placing offices will reduce the amount of sound pollution. Buildings producing noise or ground pollution should be moved away from residential areas.

The way it's phrased it would indicate that trees (from the decoration tab) help with pollution. There is no source however so I would not rely on this until confirmed reliably.

I did notice myself that offices don't have as much issue with pollution as residential buildings but whether that is cause or effect is unclear. I personally like to use offices as a buffer zone between residential areas and industrial ones.

As to how you can remove it: simply don't build anything polluting and eventually the pollution will be gone. This is also the case for water pollution -- after upgrading to clean sewage, you'll notice that the stream of pollution moves away from your river and isn't replenished.

I made a video that's posted on youtube showing the techniques I used to get the Earthloving City Achievement on Steam. In the video, over the course of about one game year, I grow the unmodded city from about 16,000 to 20,000 population while shrinking the pollution from 5% to 0.

You can watch the video here:

Sure! So basically the video shows an approach to three types of pollution sources. Industry, garbage and water pollution. For water pollution, it's pretty simple: Disperse your sewage pipes and add sufficient water treatment and boost you water budget to maximum. Water conservation policies help too which I put on my farming district only in this city. For industrial, the emphasis is on the layout of the industrial zones : which is shown graphically in the video. Basically it has dispersed zones with forests in between (Which I have found totally minimizes the pollution) and then the zones are properly supported to become high tech. Then there is the garbage breathing forest which cycle garbage from landfills to incinerators with the forest breathing up the pollution on every cycle where the incinerators are off.

The pollution disappears within some ingame weeks by itself as soon as the pollution-producing buildings get removed. Just place your industry somewhere else or use Offices instead. They're much cleaner but need more educated citizen.

Please consider that your shopping areas will need to import goods to sell if you have no industry in your city