Lakes nutrients from the rivers and brooks that flow into them. The most important nutrients for producers, such as plants, are nitrogen and phosphorous. These are essential in order for plants to grow. Lakes can be classified into two trophic lake types according to their nutrient concentration. Most Finnish lakes can be classified to be oligotrophic lakes. These lakes have a low nutrient concentration. In contrast, euthropic lakes are rich in nutrients.  

An oligotrophic lake (left) and an eutrophic lake (right).

The table below lists the characteristics of oligotrophic and eutrophic lakes. 

TROPHIC LAKE TYPES

Oligotrophic lake	Eutrophic lake
few nutrients	a lot of nutrients
clear water	opaque water
low levels of plant growth	high levels of plant growth due to plentiful nutrients
few plants	a lot of plants
fish typically salmonids, such as vendaces and lavarets	fish typically cyprinids, such as roaches
bottom-dwelling organisms few, but from many different species	a lot of bottom-dwelling organisms, but only from few different species
few birds; for example fish-eating birds such as black-throated loons	a lot of birds, such as dabbling ducks
human activity a threat to the lake's ecosystem	eutrophication transforms oligotrophic lakes into eutrophic lakes