What are they doing?

There is a big boat with a mobile crane in the canal.
I've often seen that scene a few times a year.
It regularly removes water weeds to clean the water in the bottom of the pool.
I guess it's not natural stream and it doesn't have its self-cleaning action of nature. That's why it should be taken care of to keep it clean.
It seems to cost much to maintain an artificial park.






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