The system outlined below is used by NHDES to classify lakes into one of three trophic classes. Trophic points are assigned to each lake as shown for the four listed parameters. The higher the points the more eutrophic the value for each parameter. The points for each parameter are then summed to determine the total trophic points and the appropriate trophic class, as indicated at the bottom of the table. The first parameter, bottom dissolved oxygen, is used only for lakes that thermally stratify into three layers (the hypolimnion is the bottom layer).

1.  Summer Bottom Dissolved Oxygen:
a. D.O.  >4mg/L........................................................................................	0
b. D.O. = 1 to 4 mg/L & hypolimnion volume <10% lake volume................	1
c. D.O. = 1 to 4 mg/L & hypolimnion volume >10% lake volume................	2
d. D.O. <1mg/L in <1/3 hypo. volume & hypo. volume <10% lake volume.	3
e. D.O. <1mg/L in >1/3 hypo. volume & hypo. volume <10% lake volume..	4
f. D.O. <1mg/L in <1/3 hypo. volume & hypo. volume >10% lake volume..	5
g. D.O. <1mg/L in >1/3 hypo. volume & hypo. volume >10% lake volume..	6

2. Summer Secchi Disk Transparency:
a. > 7m......................................................................................................	0
b. > 5m – 7m.............................................................................................	1
c. > 3m – 5m.............................................................................................	2
d. >2m – 3m..............................................................................................	3
e. >1m – 2m..............................................................................................	4
f. >0.5 – 1m...............................................................................................	5
g. <0.5m....................................................................................................	6

3. Aquatic Vascular Plant Abundance:
a. Sparse....................................................................................................	0
b. Scattered...............................................................................................	1
c. Scattered/Common.................................................................................	2
d. Common................................................................................................	3
e. Common/Abundant................................................................................	4
f. Abundant................................................................................................	5
g. Very Abundant.......................................................................................	6

4. Summer Epilimnetic Chlorophyll-a (mg/m3):
a. <4..........................................................................................................	0
b. 4 - <8....................................................................................................	1
c. 8 - <12..................................................................................................	2
d. 12 - <18................................................................................................	3
e. 18 - <24................................................................................................	4
f. 24 - <32.................................................................................................	5
g. >32........................................................................................................	6

Trophic Points

Trophic Classification	Stratified	*Unstratified
Oligotrophic	0-6	0-4
Mesotrophic	7-12	5-9
Eutrophic	13-24	10-18

*Lakes without hypolimnions are not evaluated by the bottom dissolved oxygen criterion.