"The Ministry of Health warns: excessive abuse of long exposure harms your frame!" 

Experiments with a long exposure, I began to get carried away almost immediately as soon as I picked up my first camera (Zenit-11). Already then I tried to shoot night landscapes, but not always it turned out. Over time, night shooting has become one of my most directions in photography and I know not about everything about long exposures, but enough!

But there are times when an excessively long exposure can only damage the frame.
On an example of two below photos - on the first exposure of 30 seconds where are completely blurred reflections of lights and they have turned to boring strips. It was only to open the aperture and make the shutter speed shorter (ISO did not want to raise up because of the noisy matrix), as reflections took shape and became a full part of the frame as a foreground. Plus, a shallow depth of field just gave the picture a space.
https://pp.userapi.com/c837437/v837437865/36cff/CmjzvGf3qU0.jpg

https://pp.userapi.com/c837437/v837437865/36d13/A8byInhFkz4.jpg

Many who are familiar with long exposure, like to blur away the water and the sky. But sometimes the blurring is so strong that there is no trace of any texture. In such cases it is better to make the exposure shorter. It was just that I once had the mania to shoot everything with excerpts of 30 seconds or more, and so, this is for those who fell ill with the same!

The first frame with an exposure of 1 minute, the second 1/20 sec.
https://pp.userapi.com/c837437/v837437865/37219/0zG7UrxRfU8.jpg

https://pp.userapi.com/c837437/v837437865/3720f/8jcuOMQ8RI0.jpg

Similarly, we can say about freezing on the river. To the ice floes do not merge into strips, but were distinguishable, it is better to raise the ISO or to open the aperture so that the exposure is slightly shorter.
https://pp.userapi.com/c837437/v837437865/397a4/0foLqqWYvNE.jpg

https://pp.userapi.com/c837437/v837437865/397cc/nsDpvrM22Kw.jpg

And if you really want stripes from ice floes, then they should be like that!
https://pp.userapi.com/c837437/v837437865/33762/C1HBhUr0ZNI.jpg

My advice will be:
    - if you want to blur water and sky, then blur it out! Do it thoroughly and exposure about 20-30 seconds will be small, otherwise it will turn out something with the prefix "under".
    - for a major blur of moving objects of nature it takes more than two minutes!
    - if you want texture and space, then do not try to blur something with a long exposure.
    - It is better to raise the ISO and/or slightly open the aperture, but get a more expressive picture.