The author is putting forward an argument to increase the budget allocated by Mason City towards the recreational activities along the Mason river. The primary reasoning of the author is that Mason City residents like water sports and they have a river flowing through their city. Although it's not currently used for recreational purpose, if the authorities invest in cleaning up the river and eradicating it's foul smell they should also invest in the recreational facilities because the residents are going to throng the place. But the evidence the author puts forward to support his claims are dubious at best.
The premise of author's argument lies in the fact that Mason City residents like water sports. Although it is stated in the essay that they indeed like water sports it's only mentioned they like it 'among' other things. This inclination is very vague because it's unclear what else do they like. It could be that they like gambling much more than water sports or maybe watching television or browsing the internet. A survey considering relative ordering of various recreational activities would be much more prudent than saying merely stating citizens like water sports. Also, are the residents actually going to spend time on the riverfront once it's developed, we do not know as there's not a speck of evidence on this aspect.
Also it is stated in the passage that the riverfront is rarely used even though people like water activities. The author assumes that this is because of the foul smell from the river. Although this may seem connected, a sound argument will would require a proper cause and effect analysis. For example only a part of the river could be smelling bad while the other part would still be okay and the residents are not using the riverfront because they are too busy with their occupations. It is one thing to like something and other to actually do it. So, again, if we know what percentage of residents actually desire to use it we will be at a much better position.
The author also assumes that the demand for water sports justifies further development of the riverside. It could well be that some part of the riverside had already been developed for recreational activities with all facilities and it's simply not used. Even if we accept the author's premise that people are reluctant to participate in recreational activities now due to foul smell and would indeed participate once it's cleaned up. It could very well be that the existing facilities would be more than enough to meet the demand considering that now it's rarely used as stated in the passage.
In conclusion, throughout the argument it's unclear whether the residents actually would like to spend time going through fun activities along the riverside and whether they are actually ready to invest their own money, indirectly through the taxes, into developing the riverside. It looks like the author is connecting the dots when in fact none seem to exist. This is a classic case of drawing strong conclusions from weak evidence and could result in huge unnecessary expenditure to the exchequer. So I disagree with the author to spend more on developing riverfront until further evidence is presented about how many people would actually be using them.