The first line of the twin Nord Stream natural gas system went into service last year. Both lines, once fully operational by next year, will transport around 1.9 trillion cubic feet of Russian gas each year to European consumers for at least 50 years.
The pipeline consortium, which has headquarters in Switzerland, said environmental monitoring of air, water, soil and noise suggested mitigation efforts were successful.
"In line with the findings of the environmental impact assessment Nord Stream's activities resulted in only minor impact with short duration," a statement read. "All set limits were adhered to and there was no tangible impact."
Littoral countries to the pipeline's route through the Gulf of Finland and Baltic Sea had expressed concern about the effects of construction during the pipe laying phase that preceded last year's launch of line 1.
The consortium stated that "careful monitoring of offshore activities in 2011 confirmed Nord Stream's construction activities to be in full compliance with environmental and water regulations."
The three sections that make up the second offshore leg are set for pressure testing and connection this summer.