The answers can be followed here bro>

https://www.google.com/search?ei=UJ41XNfeKsTgvATf_IOgDw&q=corellation+between+aquatic+vegetation+spread+and+eutrophication+AND+journal.pdf&oq=corellation+between+aquatic+vegetation+spread+and+eutrophication+AND+journal.pdf&gs_l=psy-ab.3...1710.7691..7914...1.0..0.91.1283.17......0....1..gws-wiz.c3yddp6fql8

Here is a very good paper on the subject:

Article Can macrophyte harvesting from eutrophic water close the loo...

Well,

In Stagnant water condition, the aquatic plant are likely to grow and thrive in the case of nutrient enrichment (eutrophication),The spread of plants in water also causes many environmental damage, including increased concentration of organic matter in water resulting from the death and degradation of plants, reduction of dissolved oxygen concentration, decrease in radiation energy and light intensity entering waterز

Sincerely

Dear Bayan,

This depends very much on the type of vegetation. For instance, floating macrophytes that are invasive (e.g. Eichhornia crassipes, Lemna spp.) grow on the surface, thus exerting a shadow effect on the water that limit other submerged plants and phytoplankton. When these macrophytes cover most of the lake's surface, they monopolize most resources (light, nutrients) and are favoured by massive nutrient inputs. However, submerged macrophytes do not cause (at least at the same level) this shallow effect, and then a competition for the available nutrients is established between the submerged macrophytes themselves and phytoplankton. Under extreme eutrophication, phytoplankton have advantages and can exclude most submerged macrophytes turning into a turbid phase, though some species are more effective than others under this competition,. This means that extreme eutrophication usually bring to the exclusion of submerged macrohytes either by phytoplankton or by floating macrophytes. Thus, the absence of submerged macrophytes is usually linked to high levels of eutrophication.

Concerning the percentage, I would not say that a certain percentage of coverage is mostly related to eutrophication, but instead the diversity of the submerged macrophytes' assemblages. As as general rule, which coincides for most communities, extreme levels are profited by a few species that monopolize most resources as being more effective in resource adcquisition or in resistance to the extreme conditions, thus the community is empoverished and diversity decreases. This is also true for eutrophication, with diversity of submerged macrophytes generally droping when eutrophication increases over a certain level, thus promoting the dominance of exclusion processes in the community.

Sorry Irfan , I missed your name in my response. Hope it is useful

In addition to the other comments here, it is important to note that introduction of excess nutrients (nitrogen and phosphorous) from external sources such as fertilizer runoff is usually the cause of algal and vegetative overgrowth and eutrophication resulting in the bloom/hypoxia cycle and overproduction of organic waste that eventually takes over the water body. The plants themselves aren't the cause. Phosphorous is usually the limiting factor in freshwater lakes. Nitrogen tends to be limiting in ocean environments, although the outcome is different (creation of dead zones).

Dear Irfan

Of course, there is a relation between aquatic vegetation spread with lake eutrophication, because the spread of vegetation causes an accumulation of organic matter. It is this accumulation of organic matter undegraded by microorganisms that is called eutrophication. This eutrophication could be the consequence of high concentration of nutrients (nitrogen, phosphorous...)

A relation exists not only between aquatic vegetation spread/volume and trophic status of a water body but also it is between the biometric features of macrophytes (their density and/or biomass) and trophic conditions. See:

Article Zooplankton diversity and macrophyte biometry in shallow wat...

Article Macrophyte biometric features as an indicator of the trophic...

Yes, cultural eutrophication leads to development of algal blooms and adversely affect s clean water fauna.