Impact investors are worried their sector could become too big for its britches, according to a new survey.

In the seventh Annual Impact Investor Survey by the New York-based Global Impact Investing Network (GIIN), impact investors expressed concern that the size of the impact investing industry could harm their ability to target investments that could make social or environmental change.

As large-scale firms enter the space, 71 percent of the survey’s respondents said that impact investments could suffer from mission drift or “impact dilution.” Half of the survey’s participants also were worried that capital could start to shift away from smaller intermediaries as larger companies start to dominate.

“We need to explore approaches to protect the integrity of the industry and keep impact at the forefront, while also welcoming new entrants,” said the report. “The GIIN’s vision of the market is not to integrate impact into traditional capital markets, but to integrate the capital markets into the global pursuit of social and environmental progress.”

As impact investing grows as an industry, the GIIN’s respondents expressed concern about the lack of appropriate capital across the risk/return spectrum, and scarcity of exit options.

As a result, some impact fund managers told surveyors that they were having difficulty raising capital: 73 percent of the developed market-focused fund managers said that they were having difficulty raising capital due to investors’ liquidity concerns. Emerging market-focused impact managers expressed even more liquidity challenges, with 92 percent responding that they were having difficulty raising capital.

The growth story is not all bad, as respondents did not indicate that they were feeling pressured about competition within the space. The survey participants also noted improvements in the ease of locating professionals with relevant skill sets, research and data on impact investing products and high-quality investment opportunities.

The 2017 survey involved 209 participants managing more than $114 billion in impact investing assets. Three of those respondents were major holders of impact investments responsible for the lion’s share of the assets among survey participants, totaling almost $92 billion, while one respondent declined to reveal their impact investing assets.

The remaining 205 respondents were responsible for $22 billion in nearly 8,000 different impact investments in 2016, with plans to increase their allocations by 17 percent throughout 2017 to $25.9 billion.

Most of the respondents’ impact investments, 67 percent, were made by fund managers, with a significant amount also coming from foundations, 11 percent. Banks, development finance institutions, family offices and pension funds made up a 4 percent or less of the respondent sample.

Impact investing is sometimes difficult to define because investors have targeted different impacts that they would like to make, and have also taken many different approaches to making an impact. Almost all of the survey respondents had embraced measurements of social and environmental performance using proprietary metrics, qualitative information and generally accepted metrics.

According to the survey, nearly one-third of impact investors have deliberately targeted below-market rate returns. Private debt is the most common impact investment instrument, comprising 41 percent of respondents’ assets, followed by private equity, 27 percent, and real assets, 27 percent.

Nevertheless,98 percent of respondents told GIIN that their investments had met expectations for impact, and 91 percent felt satisified with financial performance.

Impact investment products are no longer an easy way into the asset management industry. With so much recent proliferation in the space, new ETF sponsors and indexers will have to find other ways to differentiate themselves and to capture investors’ interest, according to the report.

While impact investing first caught on in Europe, eventually making its way to American institutional and then retail investors, GIIN said that it is now a fully international affair as more countries, and more investors, are interested in sustainable development and climate change mitigation.

Still, most impact investors come from the U.S. and Canada, 46 percent, and Europe, 32 percent.

The 2017 Annual Impact Investor Survey contacted 209 respondents in December and February. To be included, respondents either managed at least $10 million in impact investment since their inception, had made at least five impact investments total, or both.