What was the decrease in gross margin for the fourth quarter compared to the same period in the previous year
t secure and connected infrastructure and the future of the workplace are influencing demand. The focus of our global healthcare crisis response team is gaining momentum with an increase in healthcare awards and the pipeline across all geographies. As an example, we were recently awarded health investment in technical advisory services for a Middle East government entity and a therapeutic goods laboratory project in Asia Pacific. In the water sector, we are seeing accelerated implementation of digital technology such as smart metering, automation and remote management as well as focus on cyber resilience. While some utilities have experienced significant revenue impact during the pandemic, pre-approved programs remain in place. We anticipate periodic pauses as they reprioritize capital budget to focus on operational spend, budget optimization and digital transformation.
The environmental sector is seeing an uptick, with green recovery being pledged in Europe and in Australia, and a shift toward green energy investments in the US, which could be a growth catalyst later in 2021. Across all core sectors, our discrete solution sets are making progress, allowing us to cross sell and leverage our global market connectivity. While economic and geopolitical indicators point to continued volatility, we remain optimistic due to our resilient and balanced portfolio across core sectors and geographies and our agility responding to shifting market trends.
Now I'll turn the call over to Kevin to discuss our financial performance in more detail.
Kevin Berryman -- President & Chief Financial Officer
Thank you, Bob. Let's now turn to Slide 9, for a more detailed summary of our financial performance for the fourth quarter. Before I begin, please note that our fiscal fourth quarter 2020 included an extra week compared with the fourth quarter of fiscal 2019. While this impact was factored into our guidance, it represented approximately $100 million in a year-over-year net revenue tailwind for each of CMS and People & Places.
Fourth quarter gross revenue as a result, increased 4% year-over-year with pro forma net revenue up 2%. People & Places net revenue was up 8% year-over-year and Critical Mission Solutions declined 3.6% on a pro forma basis. The CMS decline was mainly attributed to the early impact from transitioning off of two lower margin contracts, as I will explain later in more detail. It is important to note CMS operating profit on a pro forma basis increased 14% year-over-year.
Adjusted gross margin in the quarter as a percentage of net revenue was 23.5%, down a 135 basis points year-over-year. The lower gross margin was driven by a combination of factors, primarily within People & Places, including overall revenue mix, the comparison versus a very strong year-ago quarter, the impact of some project closeout costs and the previously discussed flow-through effect of the reimbursable rate of a more efficient fixed cost structure in the LOB. The lower reimbursement rate for fixed cost is more than offset by the underlying lower level of G&A costs. This impact to reimbursable rates from our cost structure is also reflected in overall lower G&A as a percentage of net revenue of 100 basis points year-over-year to 14.4%. As it pertains to G&A, the fourth quarter continue to benefit from lower travel and employee related medical costs.
GAAP operating profit was $22 million and included $211 million of restructuring, transaction, and other charges of which the vast majority was associated with our recently announced Focus 2023 initiative and $24 million of other charges, consisting of $23 million of amortization from acquired intangibles and $1 million of costs associated with the Worley transition services agreement. Adjusting for these items, adjusted operating profit was $258 million, up 2% from the prior-year figure.
Our adjusted operating profit to net revenue was 9.1%, down 30 basis points year-over-year on a reported basis, a result of the lower People & Places margin discussed earlier. This was partially offset by improved critical
t secure and connected infrastructure and the future of the workplace are influencing demand. The focus of our global healthcare crisis response team is gaining momentum with an increase in healthcare awards and the pipeline across all geographies. As an example, we were recently awarded health investment in technical advisory services for a Middle East government entity and a therapeutic goods laboratory project in Asia Pacific. In the water sector, we are seeing accelerated implementation of digital technology such as smart metering, automation and remote management as well as focus on cyber resilience. While some utilities have experienced significant revenue impact during the pandemic, pre-approved programs remain in place. We anticipate periodic pauses as they reprioritize capital budget to focus on operational spend, budget optimization and digital transformation.
The environmental sector is seeing an uptick, with green recovery being pledged in Europe and in Australia, and a shift toward green energy investments in the US, which could be a growth catalyst later in 2021. Across all core sectors, our discrete solution sets are making progress, allowing us to cross sell and leverage our global market connectivity. While economic and geopolitical indicators point to continued volatility, we remain optimistic due to our resilient and balanced portfolio across core sectors and geographies and our agility responding to shifting market trends.
Now I'll turn the call over to Kevin to discuss our financial performance in more detail.
Kevin Berryman -- President & Chief Financial Officer
Thank you, Bob. Let's now turn to Slide 9, for a more detailed summary of our financial performance for the fourth quarter. Before I begin, please note that our fiscal fourth quarter 2020 included an extra week compared with the fourth quarter of fiscal 2019. While this impact was factored into our guidance, it represented approximately $100 million in a year-over-year net revenue tailwind for each of CMS and People & Places.
Fourth quarter gross revenue as a result, increased 4% year-over-year with pro forma net revenue up 2%. People & Places net revenue was up 8% year-over-year and Critical Mission Solutions declined 3.6% on a pro forma basis. The CMS decline was mainly attributed to the early impact from transitioning off of two lower margin contracts, as I will explain later in more detail. It is important to note CMS operating profit on a pro forma basis increased 14% year-over-year.
 Adjusted gross margin in the quarter as a percentage of net revenue was 23.5%, down a 135 basis points year-over-year. The lower gross margin was driven by a combination of factors, primarily within People & Places, including overall revenue mix, the comparison versus a very strong year-ago quarter, the impact of some project closeout costs and the previously discussed flow-through effect of the reimbursable rate of a more efficient fixed cost structure in the LOB. The lower reimbursement rate for fixed cost is more than offset by the underlying lower level of G&A costs. This impact to reimbursable rates from our cost structure is also reflected in overall lower G&A as a percentage of net revenue of 100 basis points year-over-year to 14.4%. As it pertains to G&A, the fourth quarter continue to benefit from lower travel and employee related medical costs.
GAAP operating profit was $22 million and included $211 million of restructuring, transaction, and other charges of which the vast majority was associated with our recently announced Focus 2023 initiative and $24 million of other charges, consisting of $23 million of amortization from acquired intangibles and $1 million of costs associated with the Worley transition services agreement. Adjusting for these items, adjusted operating profit was $258 million, up 2% from the prior-year figure.
Our adjusted operating profit to net revenue was 9.1%, down 30 basis points year-over-year on a reported basis, a result of the lower People & Places margin discussed earlier. This was partially offset by improved critical