Weed is a controversial subject on the waterways of Britain. I’m not talking about the stuff you smoke to get high, I’m talking about the green slimy stuff that grows in water and wraps itself around your propellor.

That’s the view from our mooring tonight. The river widens into a small lake, and it is full of weed.

The recent warn sunny days have been ideal for weed growth. There is quite a bit of it in the upper reaches of the Nene. It’s not as bad as that stretch of the Middle Level we went through last week, but I still had to go delving in the weed hatch four times today, and we will probably pick up some more backing out of the mooring tomorrow morning.

There are some boaters who are horrified by this. In exchange for their license fee they expect the waterways to be kept clear of any insidious vegetation that may impede their progress. They demand prompt action from the authorities to get rid of this green menace.

Most of England’s waterways are managed by either the Canal and River Trust (most canals and some rivers) or the Environment Agency (most of the rest of the rivers, though some like the Avon or the Cam have their own authority). (That’s the Stratford Avon, not the Bristol one.) They have somewhat different agendas.

The Environment Agency is mostly concerned about protecting the environment and flood control. The fact that their locks must provide passage for boats as well as controlling water flows from one part of the river to another is a bit of a nuisance for them. While they are able to cut weed to improve navigation, it may not always be the best thing for the environment. Because science.

Are you ready for some science? Here goes. The solubility of gasses in water gets less with higher temperature. The increased kinetic energy in warm water makes it more likely that dissolved gas molecules will escape from chemical bondage and burst out of solution. That’s why SodaStream tells you to use cold water, the CO2 dissolves better. That’s also why the amount of oxygen dissolved in the river goes down as the river warms up. You know who needs that oxygen to survive? Fish, and all the creatures that eat the fish. (OK, we don’t care about the mink, but herons and otters are cool.) You know what puts more dissolved oxygen into the water? That’s right, weed.

So, normally in hot weather the weed grows, and compensates for the loss of oxygen in the water. The fish are happy. The herons are happy. The fishermen are not happy, mind you, but that’s because they never catch any bloody fish. That’s a different rant.

The Environment Agency will cut the weed if oxygen levels are high, but they monitor them, and stop weed cutting operations before the poor little fishies start to suffocate. The boaters just have to put up with the highly environmental weed.

The canals might at first glance seem to be a different matter. They were created for navigation, so you might think that it doesn’t matter if all the weed is cut. Think again. The Canal and River Trust is a charity that only gets a fraction of its income from boat licenses and mooring fees. It has a big real estate portfolio, gets government grants, sells rights of way for buried utilities along the towpaths, sells water, accepts waste water, sells fishing licenses, and even gets a tiny percentage of its income from donations. To keep the government grants coming in they need to attract more than just boaters, so CaRT provides all sorts of facilities for walkers, cyclists, photographers, birders, poetry fans, scientists, vole fanciers, and even depressed fishermen. All of these agree that the canal would not be improved by a layer of dead fish floating on the top. Also, CaRT spends so much money on leaflets, logos, signage, and fund raising that there isn’t much left over for weed cutting.

In the financial year 2016/17 CaRT spent 41.2 million pounds on fundraising (up from 39.4 million the previous year) and 7.9 million on vegetation (down from 8.0 million the previous year). Quite how an organization can spend 41.2 million on railing funds and only get 2.9 million in donations I’m not sure. It must be another triumph of British bureaucracy.